The frame is the same, the only difference is the placement of the motor mounts. The four bangers sit farther back than the sixes. I dont know the measurements at this time but can take some off my four in a bit if needed. If the new one looks like your old one you should be just fine.
90 YJ 5.2 Magnum, AX-15, 231 SYE'd
D44 front, welded/trussed AMC20HD rear. 4.56 gears soonish.
Western 6 lug aluminum wheels, with 35x12.50x15 Wrangler MTRs