I would like some suggestions on how to gain some extra space in the rear of my car to put an 11inch rim out back. With the spring being the main concern.

 

Move the springs inboard. Depending on what car you have, you may be able to get prefab mounts. You need to be skilled in welding and have the patience to study the geometry of the suspension components. Best bet is to get together with a good machinist.

 

Do any of our vehichles have prefab mounts available for them...say perhaps for 87 birds? I would love to fit some 11's in the back....or more.

 

Check with Competition Engineering, they have quite a few. Problem is, coil springs are much more difficult to work with than leaf springs due to the control arms.
No kit makes it easy, you still need to know your geometry and dynamics and know how to weld. If you are off just a tad, that translates to a lot over the length of the car.

 

you can fit an 11" and bigger rim on 3rd gens with minor mods (rollinf the fenders and removing the inner lip on the back of the wheel well) and the correct backspacing.

good luck
anthony