This is for E-body...
When you move the springs into the frame rails and use offset rear hangers,
what is the new spring perch distance ? Center - to - center.
Factory E-body is 46".
f you move the spring in 3" per side using the frame rail kit, the new perch center to center would be 40".
If you move the front eye into the rails, there is a corresponding rear rail offset rail that allows the shackle to be the regular vertical kind. There is not a 3" offset shackle that allows the front eye to move into the frame rail while retaining the original shackle mounting point. If you look closely at the rear view in the linked USCT site, you will see this rear frame alteration.
If you use the bolt in, 1" offset front hangers, which do not cut into the frame rail, you must also use the 1" offset shackle kit.
Keep in mind that the rear frame rails in an E body are splayed wider at the rear. You can only move the wheel tub in about an inch, maybe 2, before you will now have frame rail interference, regardless of where your springs are located
