Jay - 

Y'know, when ya buy an exhaust system, any exhaust system, the supplier
should provide the gaskets.  I've gone round & round with some of my
suppliers about this for the past year (Bugpack in particular).  Anyway, head
on down to the nearest FLAPS and buy VW Part # 043-251-509 (2 of 'em).
 They're triangular in shape and metallic in composition and this should bolt
up yer new exhaust to the heater boxes on yer 78 Westy.  Fits all buses
75-78.  Paper gaskets aren't recommended, nor Permatex as the heat is just
too high.

We carry these gaskets @ about $3 ea.  Prices could vary place to place.

Jim / BusBoys@aol.com