"Federal's had no O2 sensor and even though I added a bung the O2 readings
have been unreliable"

Hey Tom,

I also welded a bung into the exhaust of my 1982 air cooled Federal Westy.
I installed one the of the Bosch O2 sensors sold by Bus Depot.  My
readings are pretty solid above 30mph.  Anything below 30mph and the
sensor is not warm enough to produce a signal.  My readings start at about
0.6V at 30 mph and steadily increase to 0.9V at 70mph.  I am very
interested in comparing these numbers to another Federal van.

What kind of numbers are you getting?  Is the O2 sensor good?

Jake