Maze is correct. The 6cyl has an AX15 behind it, and the 4cyl is an AX5.
The clutches aren't the same size, and neither is the splines on the output shaft going to the T-case.
'87 YJ, 4.2L built and bored, 8.5" of lift, 8.8 rear, AX15/NP 231, Tom Woods drive shafts, Flat fenders, 12,000LB winch, Custom bumpers, Rattle can paint job. Never completed...