Good questions all John.  I can't help on the engine transplant questions
but can give this based on my personal experience.

>
> First, what were the major differences between model years of the
> Westy Vanagon?

'80 through the middle of '83 aircooled, 83.5 thru 85 1.9L WBX w/Digijet
(open loop) EFI, '86 thru '91 2.1L WBX with Digifant (closed loop) EFI.  '86
and later have better brakes also.  And I will add noticably better brakes
when comparing my '85 to my current Westy, a '90.  And very noticeable
difference in power with the 2.1L engine.  Disadvantages of the AC engine,
lack of power.

There are some minor but to me noticable difference from about '88 on.
Changes in the air conditioning layout,  better upper canvas in '90 and '91,
minor but nice change in the hanging closet door, elimination of the OX
counter and warning light ('88 on??)  , addition of the flow through
ventilation, and better looking  (but fragile) fiberglass bumpers. And oh
yea, the '90 and '91 have a refrigerator that is MUCH easier to light (but
over time has the same cooling problems as the earlier models)

--
Loren Busch
"I ordered a feast in the hope that you would come."
"I came in the hope there would be a feast."
(From "Monument" by Lloyd Biggle Jr.)