I think I may have solved the infamous engine swap vibration.  I have a 1.8l digifant in my 82 diesel Westy.  I used all the original diesel mounts, etc.  I had a vibration between 3000 and 3400 rpm.  I installed a modified mid 80's Jetta/Golf motor mount on the left side.  Here is a link:

http://home.jps.net/~zezoff/vanagon.html