I found this link for a company that puts Mazda RX-7 rotary engines in
Vanagons.
Thought I'd pass it along.

http://www.atkinsrotary.com/engineQA.htm

I recall that someone on the list was asking if this could be done. I
wouldn't think it would be all that good as rotary engines are not known
for their low-rpm torque.

Here is what the webpage says:

I have a 1988 VW Vanagon in pristine condition but with a rotten water
box motor. Is it feasible to swap in a Rotary?

Hi,

We have done this in the past with wonderful results. For more
information please call Dave at 253-848-7776