Although my 86 started life as a bilstein equipped base suspension car, my 85 parts car, graciously included with my car when I bought it in Dec. is a Z51 equipped car.
I managed to strip all the good parts off the car. My car is now equipped with the front spring, lower Z51-marked control arms, both swaybars, quick ratio steering rack from the parts car. For the rear spring, I used the vette brakes sport rear spring, which from what I understand is supposed to be around the same rate as the Z51 spring. I was not able to get the original Z51 front shocks off the parts car due to 17 years of Okinawa tropical island rust that apears on any car that sits in the back of a dealers parking lot not running for who knows how long. My car's shocks were replaced somewhere along the line with KYB's but I will eventually replace them with some Koni's or Bilstein sport shocks.
The car rides quite a bit harsher, but I have never complained of a car that I can feel the road with. It seems to be much more precise feeling, probably due to the steering rack. The car seems to be much closer to neutral and more easily steered with the throttle. All the hints of understeer in the original suspension has vanished.
For all you C4 guru's out there, have I missed anything from the Z51 suspension? My car was already equipped with the options that the Z51 specifies, like the heavy duty radiator, oil cooler, and the booster fan. I am also running 17x9.5" ZR1 wheels with 275 40 17's all the way around.
Thanks for the help if there was anything I missed.