Yes 90 bii in ca had mass air
If memory serves the 2.9 was actually available in ca until the end of the run of the 92 ranger
I have seen one mas air equipped 2.9l in all my years, it was in a junk yard in colorado
That is why I ask because they are so rare.
However in theory if you had a mas air 2.9 you can easily convert to 4.0 by piggy backing the dis ignition in place over the factory 2.9 harness and ditch the distributor
Wiring is a part of any conversion
Do not use Haynes manuals instead buy the factory wiring books
I will be wiring a 96 4.0 into a 89 ranger very soon, I will post up all the details of this job
I believe the 2.9 was actually still around until 91 in some rangers
It was rumored that some 90 bronco ii actually came w a 4.0 however it is very hard to tell because it is so easy to make a 89-90 bii look like it had a factory 4.0 since they are both so close in 1990-92, not much changes under the hood aside from it either had a 2.9 or a 4.0, the under hood layout,
Power distribution wiring, battery location, plumbing, etc is all very very similar
My favorite way to convert a 86-90 bii to 4.0 is to use the power distribution wiring from a 93-94 truck along with a 93 4.0 intakes and computer. The 93 4.0 has an excellent power distribution box, 93 had no cam sensor and no egr (except in ca).
However there are many ways to get a 4.0 under your hood. In a perfect world I try to use the later 4.0 like from a 98-2000 ranger/explorer along w the sohc clutch and sohc 5 speed m5od.
We have and can also convert the old 2.9ntrucks to use the obd2 96-2000 4.0 computer if necessary.
Every swap is different, chances are there will be at least some minor wiring if not major changes needed