I put a lot of thought into how to spring the car. I drive a lot of very low vehicles and nothing makes me crazier than a low car that rides like a jackhammer. It is possible to make a very low car ride reasonably comfortable. My big Buick Riviera, for instance, rides 2-3" off of the ground and you wouldn't know it while riding in it. I also had the space constraint issues of only having about 12" from the floor to scrubline. I originally wanted to make some sort of bellcrank setup with qa1 coils but the lack of space made every design too much of a compromise. I played around with the idea of a transverse leaf and looked into corvettes. I had already figured that I needed a spring rate of about 235 lbs/in or so and it so happens that one particular year of corvettes had a rear rate of 229 lbs/in. I found a spring on ebay for $100 and went to town. These springs weigh about 10 lbs and do not fatigue like a steel spring.
Spring had to be narrowed, I cut an inch and a half off of each end, redrilled and rebonded the end plates
This is the difference in width. The spring rate change is negligible.
The stock corvette style of attaching the spring to the spindle wouldn't work because there is some misalignment that the bushings wouldn't like, so I built a heim and shackle linkage.
Then I built the mounts on the spindles/arms
Clamped the spring in place for a mock up run, and it sits and articulates fine.
My 13" Advans barely fit. I had to dolly the lips over and portopower one fender out a bit (I think it was pushed in from the accident it was in) and now nothing rubs at all.
I don't have any up to date photos yet, It is almost done now. Shooting to be at cars & coffee in Irvine a week from this Saturday. Fitting the gas tank today, then I just need to finish shortening my 280zx struts and running my exhaust. Here are some photos from when I was finishing the IRS subframe and spring perch mount.