14 bolt rear in a 68 ???'s

[WHITE-NOISE]

well im basically doing a frame up build on my 68 4x4 longbed, first i started with a nice set of torches and got rid of the eaton rearend and the cheezy old worn out leaf springs and the death trap closed knuckle dana 44! swapping a 60 front and 14 bolt disked rear and 1 ton 56" rear springs from an 85 military truck......well i got the springs hung and axle center back where it should be but it never dawned on me that the 68 frames are skinnier than the 80's body chevys and i have to move my spring pearches....

my question is does anyone know how much i need to the perches in...i know theres alot of people that have done this swap and im hoping someone might know the measurements, i already got rid of the old rearend or i would just measure it off that.