Well, I called around, and although I did find a crossover pipe for my '81
Vanagon through an aftermarket supplier (Bus Boys), it cost about $10 more
than what the dealer was asking....no help there.  Since cash is tight, I
decided to take a risk and go with the JC Whitney model for now, which cost
$72 with shipping vs. $427 from the dealer.  The Whitney system replaced
everything from the heater boxes back, an added bonus, since lately the
muffler kept separating from the catalytic converter and allowing fumes
to escape.  I do plan to hold onto the other exhaust parts, just for luck....
no, actually, in case I come across a used cross-over pipe and find that the
stop-gap JC Whitney system doesn't cut it.  If anyone comes across a suitable
cross-over pipe (y'know, they seem to pop up everywhere ;-)  ) PLEASE let
me know.  I'll keep you posted as the saga continues to unfold.....

Thanks to all who offered advice on my woes!

Andy