I have a set of used AUDI Ronal 10 Spoke 15" rims for sale.  I use 215x75-15
BFG AT-KO tires on the early SA rims.  They're a bit tougher than their
competitors, have very good wear characteristics, but they're noisier than
the "Mice"-lin comparables,  Seth at H&R motors has michelins as does Warren
Christensen of the subaruvanagon list.

I can supply you with a spreadsheet that will demonstrate the effects of the
tire change on your
vanagon with respect to rpm vs mph.

cheers,

pensioner