So I'm going to have to resurrect this old thread here for a bit.....after my PS box on my CJ started leaking, I decided to make the swap. Bought a reman'ed J20 box (fingers crossed that it is in fact a J20 and not something else, but still better than what I currently have, a leaky box) and mounted it up. My PS coupler doesn't work on the input, no surprise there as that was discussed in the swap. The coupler is larger than the input shaft on the gearbox.
So I want to confirm that before I drop $40 more bucks on this and/or dig through my box of misfit parts for my manual coupler (from when I swapped from manual to power two years ago) that the manual coupler is smaller than the power steering coupler? The input shaft on the gearbox measured a shade under 3/4", as mentioned above by JeepnTXJ, 0.720" would be about right.