If you do the 4.0 swap into an 89 or 90 B2, then it's a plug and play swap
AS LONG AS you get
ALL the underhood wiring.
Simply remove the 110 pin connector w/ a 10mm bolt in it, and install the 4.0 underhood harness. You also need to go through the firewall on the pass side w/ the 2 rubber grommets...again, remove the 2.9 stuff and install the 4.0 stuff. Use 91-94 for this type swap to work.
But remeber this....91 and 92 4.0's have a
round engine to underhood harness connector and 93 and 94 have a
square one. They don't interchange (Actual square peg/ round hole deal), but are wired exactly the same.

Why they swapped the shape of the connector I do not know