zero rate kits

[jakeblues652]

so first off, do they make one of these for the rear of my '67?! i have been told that the front springs are 2 1/2 and the rear are 2 1/4, and ORD only makes then for 2 1/2" and 3", that is if im on the right page.

second, can i install one of these just to give lift, not to offset the axles any?

what would be the pros and cons to this system (if possible), and what would i get out of moving the axle an inch??