IM Not So Expert O, The 2.5 would be my choice for shoving in there if swapping the mounts and electronics are the only differences. It's supposed to be a really solid engine, if not as powerful as the 4.0.

 

Ever road in a jeep with a 2.5? It is extremely slow and you always have to keep your foot in it. The 2.5 I drove was mated to a 5 speed and there is no point in even having 5th gear. It does not even come close to a 4.0l. The 2.5 feels like it has half the power of a 4.0.

 

Very true, but from what I understand, 2.5 > 2.8.
Besides, it's a Jeep, slow and expensive is what they are.

 

some numbers to throw into the mix:

Weight:
2.5L - 340 lbs
2.8L - 350 lbs
4.0L - 515 lbs

HP & TQ:
84-85 2.5L I4 carb - 105 hp @ 5000 rpm, 132 ft lb torque @ 2800 rpm

86-90 2.5L I4 TBI - 117 hp @ 5000 rpm, 135 ftlb @ 3500 rpm

91-00 2.5L I4 MPI - 130 hp @ 5250 rpm, 139 ft lb @ 3250 rpm

84-86 GM 2.8L V6 - 115 hp @ 4800 rpm, 150 ft lb @ 2400 rpm

87-90 4.0L I6 EFI - 177 hp @ 4750 rpm, 220 ft lb @ 4000 rpm

91-95 4.0L I6 MPI HO - 190 hp @ 4750 rpm, 220 ft lb @ 4,000 rpm *96-01 - 225 ft lb torque @ 3000 rpm