Originally Posted by skizriz
Exactly. Stock YJ shackles are 1" longer.
Stock cj shackles are 3" eye to eye.
The 3.5" YJ springs would be factored with 4" shackles.
So you would need 5" shackles to reach your 4" of total lift.
You're over-thinking this. The shackle length has nothing to do with how much lift the springs give. Using the 3.5" springs is going to give an additional 3.5" of lift over stock springs regardless of the length of the shackle, as long as the shackle length remains constant.
So 3.5" springs on a CJ will with stock CJ shackles will still give 3.5" lift. Add 1/2" CJ lift shackles to net a total of 4"
77 CJ-7- AMC 360, Edelbrock cam, MC2100, Fenderwells, CJ T18/D20, Chevy D44/EB 9" rear, Trutrac f/r, 4.11, SOA, 1.25 lift shackles, 35x12.50 BFG KM2s, Shackle Reversal