Lisa,
 
 Sorry to hear about your heat exchanger woes.
 
 I'm taking a pretty big step away from the buses I'm familiar with but
 here goes: I believe that the right hand heat exchanger is the same on
 both the 49 state and California air cooled Vanagons. This heat exchanger,
 the muffler and tail pipe are the only exhaust system parts that the 
 two versions have in common, I think.

 Perhaps you could use the right hand exchanger that was sent to you from
 AVP with a left side exchanger obtained from a 49 state Vanagon. What 
 kind of shape is your collector and "U" pipe in? Some of the exhaust 
 system parts may be shared with the '79 bus <that year only> but not 
 the heat exchangers <buses got some of the heater air from the fan housing, 
 Vanagons get it from that plastic fan on the alternator.>

 Good luck!

 Dave
 '74 Westfalia