Does anyone know the heater tube size on a '68 bus - the single center tube. 
 From what I could see, it looks to be 3 inches.  I'm ordering a helper fan 
from West Marine and they offer both 4 and 3 inch sizes.  Could a 4 be 
adapted?  Might give even more flow.

Thanks,
Dean Aukes
'68 Pritschenwagen mit Doppelkabine
'73 Campmobile