When choosing a replacement distributor,should one choose one with a single or double diaphram. What is the difference in performance? Thank you

 

Single is simpler. But if you want to restore it to original go with a dual and research all of the routing.
I'm aware of no performance difference. The dual provides different advance while the engine is still warming up.

My compliments on your spelling of DISTRIBUTOR.

 

If I recall correctly the purpose of the second diaphram was to retard the spark at idle for emission purposes.

If you're going for show hook it up (Possibly block the line.

If you're going for go use a single. Better yet get on which is stock pre '67.

Everyone should remember that 67 started the emission stuff--Emission control and gas milage/engine performance are incompatable.