You need more than just the engine. You need the correct ECU, complete wiring harness, ignitor, main and fuel pump relays and more. The best place to start is by reviewing all the files in the Subaru/Vanagon yahoogroup and this site
http://www.weidefamily.net/vanagon/
The '90 engine is an OBDII engine, a little more work with the wiring harness. I have a 2.2L Vanaru Weekender. It runs great but I hear that for the Synchro, especially a Westy, the extra HP of the SOHC 2.5 is preferable.
However, the 2.2 is a great little engine. If it indeed only has 85K miles, that is right in the sweet spot.
-Kent
Concord, NC