I just did the same thing to my Scrambler, I used '78 Scout II axles, so I had to move the perches as well, albeit they are leaf sprung and not coils, but the same idea should pertain. I moved the rear perches but left the front intact, I just moved the springs outside the frame, pumpkin got in the way and I didn't want to shorten the axles or have one side 4" longer than the other.
I measured the old axle and got the exact width between the perches, checked them for center against the pumpkin. I had to move the rear perches 1.75" inward on the Scout axles to match the same track as the CJ. I then set up both axles so the perches were level. I then welded a reference tab using 1/4" steel to both sides of the Scout axle so the tabs were inside of where the new perches would be, level, and equidistant from the pumpkin. I then cut the old perches off, measured the remaining distance to the new perches, leveled them, and tack-welded them on. I did not re-use the old perches but bought new ones. I'd cut the old ones off carefully so you can weld them back on. I then checked my measurements and leveling, and fully welded them into place. All in all it was a relatively short procedure, I spent more time measuring and re-measuring to make sure I got everything right. When I was done I cut the reference tabs off and grinded everything down, then painted with Hammerite for a sturdy finish. I hope this helps and your conversion goes well.
'97 TJ Sport
'81 CJ-8 Scrambled!
'71 Commando SC-1