Does anyone know which master cylinder to use when swapping from a single to a dual cylinder on a 65 chevelle 300 non-power 4 wheel drum system

I'm not sure here, I couldn't imagine why you could use a master cylinder for say a 1967 with non power assisted drum brakes. That should be a dual bail master. Double check to make sure it'll bolt up, but if it does, you'll be good to go.

Any master from a 67-72 chevelle with 4 wheel drum brakes should work. I would also grab a distribution block from one of these cars when you split the system so you will also have a brake warning light if there is a system problem (I know, like your foot wont tell you there is a problem smile.gif )