"... This leads to rapid and noticeable changes in kinematics when compressed further. ...This car is NOT designed to be lowered to this degree. ...to change the kinematics to favor a bit of squat and body roll.".

what you means by changes in kinematics ?
without going back to functional dynamics with compensation arms?
or what arms ?

For the camber associated with lowering, there are solutions to add positive camber, to make the wheels vertical, like oem for extrem street use.

For example, I'm thinking of lowering between -36mm and lower... -50mm, with original tires 245/275. approaching a camber of -1.8° to -2° (with ou add positive camber) or more...-2.4. there are solutions to add positive camber. not trackday. 12k or less rear. 14k front. with add positive camber, i will like to obtain 1.2° front, 1.6° rear.

Does your knowledge of the maximum lowering impacting kenimatics permeit this to be resolved with more add positive camber ?

what would you estimate as the maximum lowering to save the kinematics?

with all alignment problem solved, to original alignment, will the kinematics no longer be functional in dynamics?
or.
with or without to add positive camber, what is the maximum lowering limited by functional in dynamics ?

Thanks
Best regards
Xavier

Just modify the rear subframe pickup points to reduce the extreme camber when lowered. It works very well. I have one.

is this a street car or a track car?

A lowered Z34 has rapidly increasing rear camber in bump. If the car is rolling into a corner with no rear bar, you may find you are only getting half the rear tyre on the tarmac in mid-corner and you are trying to put power down thru 5 or 6 inches of rubber.

It may be that standing the tyre up a bit might be the solution

I have a 500hp (hubs) Z34 that runs 250/650R18 Yokohama slicks on a 10" rim and I have good balance with an OEM rear bar. I run MCA double-adjustable shocks (made in Australia by a former Australian Rally champion) and I'll check my current rear spring rate when I get home tonight (on the train on the way to work at present).
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We found we had to lift the rear given the camber curve once we'd lowered the rear ride height to where we initially thought it should run. Eventually we found balance but our early lesson was "you can go too low" with OEM suspension dynamics

Softer rear spring will only exacerbate camber increase in roll but harder spring rate will kill squat which gives you drive and the end result will be a very twitchy car.

Do this and you can stay low. I have a modified one on my car and it is awesome. I can hook first and 2nd. It put a stop to the top fuel burnouts. It works. Do both mods. Upper control arm and the Traction link anti-squat mod.

Is this why so many track folk have come to the unintuitive conclusion that a bigger front bar actually helps the car rotate?