I can't comment on the TBI compatibility, but I did have a '90 short-box 2wd and thing was an absolute dog. Can only imagine how much worse it would have been as a 4wd. So, honestly, I think you are fighting an uphill battle if you leave the 318 in there.

The 360 in '91 was TBI and I drove one: it was pretty strong and wished that's what I would have bought. I think you should go the 360 route: it will be cheaper and less frustating in the long run than fooling around with that 318.

Also had a similar truck to yours: an '86 318 2bbl with a bit bigger tires and lift: it needed a 360 too.