the spring is there to hold the car up , its the shocks job to control the compression and extension rate not just at the rear but at the front of the car too .
low buck the cargo and a bag work
on murphsters white T and my 86GN i run 12-150 coils with a wolferacecraft adjustable perch for ride height adjustment adding around an inch or so for 27" ride height with a 28 tire (mt pro 275), you could run spacers under spring to find a happy place , you could install the adjuster up on the frame perch or on the axle tube but if on the axle you may need to add a piece of tube to the top to prevent spring drop out with some over extending shocks (like the comp engineering). Murphster has been running the strange double adjust rear shock and i just changed out my singles for doubles
if a car is going to squat the spring cant change that but the shock can slow it down or control what happens when its stops
we run the upper Instant center relocate setup (baseline) and that setup can be adjusted to prevent rear squat on launch and youll actually rise slightly on launch but again the spring is there to hold the car.. the shock controls the speed of the change , spring can be stiffened beyond whats needed for ride height almost to the point it will prevent a hard squat but it cant prevent rebound
my 87gn i have IC relocate GNS ridetech coilovers single adjust front and rear , Scot W handled the spring choice and they seem to be working
