1)
http://www.naxja.org/forum/showthread.php?t=70388. Loads of good information in there (the bushing you want, if the AX-15 pilot is significantly larger, is the early 1970's CJ V8
three-speed, by the by.)
2) To convert an "internal" AX-15 (AX-15i) to "external" (AX-15e,) you need the bellhousing, clutch fork, fork pivot, and front bearing retainer - in addition to the hydraulics. The friction is the same all the way up. Some of these parts can be difficult to find.
3) The hydraulics, per reports from the field, will drop right in. I have yet to personally verify this, but my 88 will be getting an AX-15e as part of its refit. I will also be assessing the possibility of swapping the earlier input shaft in, to eliminate the pilot confusion.
The break point seems to be 1993/1994 for going from AX-15i to AX-15e, and (interestingly,) the smaller pilot is available until at least 1993 (again, per reports from the field.) The AX-15 was used in a few light trucks, so it's just a matter of finding one and then finding an AMC bellhousing for it (in case you can't find a compleat unit, you can assemble one piecemeal.) The AX-15e bellhousing also fits the NV3550 - again, this is a reasonably common light truck transmission for Chevvy and Dodge.
But, start out with the thread I linked to, and go from there.