So… the 4.0 will bolt up. The trans may or may not last long, but it’s easy enough to get a 4.0 trans.
The biggest thing is the wiring. You are going to have a ton of it. You need to use the 4.0 wiring and computer. You will either have to swap the dash, replace the dash harness, or splice ALL of the dash wiring to the new harness. 83-88 Rangers/Bronco II are the most difficult to do, IMHO. Lots of them have been done, so there’s plenty of information on it, and I started a swap on my 88 only to abandon the idea and change directions. Part of that was the difficulty of the swap (at the time there was a lot less information available on it), and most of it was driven by needs. My 89 needed the power from a 4.0 to drive the 35” tires. My 88 just needed a motor (resto-mod rather than lifted). 89 used the same dash harness as the Rangers that got the 4.0, so the swap was much more plug and play. My 88 is getting a lot of the goodies I’ve heard about over the years. Shift kit and other mods for the auto transmission, 2-3” of lift (enough to make it easy to work on and clear 30-31” tires without a fender trim), extended radius arms for ride quality, electric fan, electric power steering, and all the 2.9 mods I can cobble together (headers, MAF conversion, porting on heads and intake, free-floating rocker arms, etc). My ideas for the motor may change some after reading a bunch of stuff from
@gaz and
@PetroleumJunkie412 , but basically trying to build the thing to appear stockish but be upgraded for fuel efficiency and performance