In general, the object is to lower the car to reduce weight transfer and give maximum cornering grip – without going so low that handling deteriorates.  For street use with a maximum emphasis on track work, with 205/50/15 – 225/45/215 tires, the car can be lowered so that it measures ~ 12 cm (4.5”) from the ground to the bottom of the “frame rail” at the point where the tie rods come out of the engine bay.  Much lower than this may cause problems with the geometry and will work against good handling (camber gain & bump steer among other things).  However, for street use, you’ll have to be careful regarding ground clearance (manhole covers, storm drain grates, speed bumps, etc.).  For general street use, I would suggest lowering a little less – maybe as much as an inch less – a little less than stock but safe on most roads.  As to balancing front and rear ride heights – the ideal way to set front and rear ride heights is to scale the car and adjust ride heights to even corner weights.  Since this may not be practicable, you can use a rough rule of thumb of fronts being .5-1cm lower than rears.  Since for most cars with fixed rear springs, it is hard to adjust rear ride height lower than the spring gives, it is easiest to measure the ride height at the rear and then adjust the front ride height to be lower.

If the car still has them, it is easiest to measure at the jack point bottoms (it is not the way the factory manual calls for, but it does work) – perhaps 15 -16 cm at the front jack point and 16 -17 cm at the rear (this is the same for all models. For a general use streetcar, the lowering should be limited to a point where, when loaded, the front lower control arms are parallel to the ground, or slightly up at the outboard end. For dedicated track use, lower is better, and as always, some experimentation is a useful thing.

On late GTV 6 and Milano, the rear torsion bar mount is fixed to the car in a specially reinforced section of the unibody.

Stock bars can be removed to the rear as per the manual.  However, torsion bars larger than 25mm can only be removed (or installed) from the front and require removal of the lower A-arm as described here. All positioning and adjustments must be made by removing and replacing the lower A-arm.

1. For reference – measure the resting ride height before doing anything.  On a flat surface, measure ride height from the top center of the front fender well lip to the ground.  This should be roughly: Milano ~ 25.5” GTV6 – 27 to 28 inches. Or measure to the bottom of the jack points as mentioned above.
2. Jack up front of car as high as possible, and support chassis with jack stands – or if you can, put on lift.
3. Remove wheels, disconnect both ends of the sway bar links from the control arms, and disconnect shocks from the lower control arms. Disconnect the calipers from the spindle (make sure they are supported), but it is not necessary to break the fluid lines. 
4. Remove cotter pin, retaining nut, and using ball joint separator, disconnect the steering tie rod end from the steering knuckle.
5. Remove both plates from the back side of the torsion bar cross member.
6. Jack up the lower A-arm at the outer end until the upper arm moves away from the rebound stop and the car just begins to lift off the jack stand.
7. Remove the cotter pin, back of the retaining nut and then, using a ball joint separator, disconnect the lower A-arm from the spindle.
8. Lower the A-arm until it is at full droop.
9. Unbolt the suspension lower A-arm from the body pivot clamps. Note the position of the spacers.
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10. Slide (hammer) the suspension arm forward off the torsion bar. Remove the torsion bar from the rear mount by pulling (driving) it forward. You may insert a bolt in the threaded hole in the rear of the torsion bar and hit on it to help in removing the torsion bar. Do not hit the end of the torsion bar directly.
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11. Lubricate the splines of the new torsion bar with anti-seize compound or moly grease.
12. Reattach lower control arms.  Raise the lower A-arm to a position that places it either slightly down at the outboard end, or parallel with the ground. 
13. For an initial setting to obtain the approximate suspension height: By trial and error, while keeping the control arm at the approximate height you chose, rotate the torsion bar to find the spline alignment that permits the torsion bar to engage into both the front and rear splined sockets easily.  The torsion bar must be started in the splines by hand but may be pounded to fully seated position after initial engagement. 
14. Slip (pound) the bar into the splined socket in the rear mount (the end with the threaded hole to the rear).
15. Install the lower A-arm onto the bar and then onto the car.  The spacers removed in step 9 are for camber adjustment.  If you select a lowered ride height, these spacers will be too tall to allow proper camber adjustment.  It is a good idea to grind off about 5 mm to give adequate working room so camber can be adjusted to a correct setting.
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16. Re-assemble the upper and lower A-arms to the spindle.  Connect the steering links loosely.  Leave sway bar, shock absorbers, and brake calipers disconnected.  Install wheels, and lower car to ground.  Roll car back and forth and bounce front end to settle suspension. Now, check the position of the lower control arms and measure the height from ground to your fixed reference point. It is unlikely that overall ride height will be what is desired or that the height will be the same on both sides. Not a problem.  Write down the height for both sides.  Jack up car, remove wheels, disconnect steering link, and disconnect upper and lower A-arms from the spindle.
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17. For reference, mark the positioning of both the front and rear ends of both torsion bars by marking a spline and a corresponding point on the spline socket.
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18. Final adjustment to the desired ride height is done as follows. Looking forward from the rear of the car: Increase Ride Height – the ride height is increased 2.5mm (0.098″) by rotating the torsion bar one tooth at each end.  Right side of the car, clockwise.  Left side of car, counter-clockwise. Decrease Ride Height – the ride height is decreased similarly, but rotate bars in the opposite directions.
19. Calculate the required change in spline count and mark the new bar spline location (on both ends).
20. Move the bar at the rear so that the new marked splines match the socket marks. Insert bar into rear mount, then adjust control arm position as needed to match front marks to fit.
21. Check ride height again as in the direction #16.  Make further corrections, as necessary. After desired ride height has been obtained, re-assemble all components.
22. When the ride height is changed, front end alignment will be changed drastically and so should be realigned ASAP.  Toe and camber will be most drastically altered.  Most adjust toe to near zero and adjust camber to be somewhat negative.  However, caution should be used.  For a good starting point, see owner’s manual for toe-in/toe-out, camber & caster specifications.

Example: Desired ride height (fender well lip to ground) 26″. Preliminary height R.H. side 26 3/4″ (3/4″ too high). L.H. side 25 1/2″ (1/2″ too low). To correct height on R.H. side: 3/4″ (.750 / .098 = 7.65) or approximately 8 teeth at each end. Mark 8th tooth at each end of torsion bar, and match to previous mark on splined socket. Raise lower A-arm until torsion bar slips easily into splined socket. To correct height on L.H.side: 1/2″ (.500 / .098 =5.10) or approximately 5 teeth at each end.  Mark 5th tooth at each end of torsion bar, and match to previous mark on splined socket.  Lower the lower A-arm until torsion bar slips easily into splined socket.