Unfortunately a Vanagon with a bad head gasket is not a rare item.  The value
of such a vehicle is rather low, I would say $1000 at most, more likely
$500-800.  So selling is not really an option.  Replacing the motor with
another Waterboxer, to me, would be a mistake.  You could replace it with a
rebuilt Chevy V6 for less than replacing the waterboxer and when you are done
you will have more power and no more "head" aches.  If you want more info on
the conversion write me back.
Thanks
Ken Wilford
PS You could do what I did if you are really strapped for cash like me.  Go to
a local racing or speed shop.  Buy a bottle of Moroso Ceramic Block Sealer.
$14 Follow the directions on the back.  Drive around for another 6 months to a
year until you can afford to do the work.  Sometimes this stuff lasts for
years.  It makes Bar's Leak look like toothpaste.  It is a miracle in a
bottle.