"ROUGH measurements of Honda engine length show it might fit the
Vanagon engine bay (though what looks like the cam(s) position sensor
juts into Vanagon firewall) and height from crank OC shows engine may
fit under lid. (though did NOT measure down to oil pan bottom). The
coolant hose in/out looks similar to my ABA so that's not an issue."

This reminds me of something I did way back when. I would encourage
the curious, but would advise correcting this before doing anything
else:

"(though did NOT measure down to oil pan bottom)"

I would think you'll find the rest of the effort vastly more
troublesome and time consuming than this, and perhaps precluded by it
as well.

Cheers,

Jim Akiba