You basically want everyy inch of wiring under the hood from a 1990-92 Ranger with a 4.0.
And you want the wiring that goes through the passenger side of the firewall to the computer and heater blower switch connections and inertia switch.
Done that way it literally all plugs together. The bellhousing, motor mounts,
exhaust y-pipe, lower radiator hose are ALL exactly the same.
Anyone who can replace an engine with an identical engine
will only find an extra day of work to swap a 4.0 in for a dead 2.9
that presuming it takes a day to get the dead one out and a day
to put the new one in the chassis.... AND you got all the stuff that's
different
Swapping in the throttle cable, upper radiator hose, air box (fits in the same bracket)
air duct, and swapping out the harness is tedious, but not particularly difficult.
AD