Here's what Tom Wilson's book has to say about the relevant differences (in
this case) about the 2000cc engines used in later busses and early Vanagons:

"Up to '78 all Type 4 heads used almost round exhaust ports.  So called
Vanagon heads dating from '79-'83 use more rectangular ports.  Port shape
also changes exhaust pipes, so engine swaps should include at least heat
exchangers."

From: "Michael Heron" <Michael.Heron@MBS.GOV.ON.CA>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, April 20, 2000 5:15 AM
Subject: 81 engine in 77 bus?

Does anyone know/have any experience in how straightforward it is to put an
81 vanagon engine into a  77' bus? I would like a job that requires minimal
amounts of replumbing etc.
---------------------------------------------------------------------------
Tom Young                  tomyoung1@home.com
Lafayette, CA 94549    '81 Vanagon
---------------------------------------------------------------------------