Master cylinder?

Youro master cylinder might have been changed, anything can happen in 30-40 years of a cars life.

I'm trying to order up a dual disc/drum master cylinder from my local Napa guy and he keeps getting the wrong thing, even though the Napa computer shows the master cylinder I want, he gets the wrong thing in the box. The last one he got for me (just today) was the exact master cylinder you're showing up above! (but a nicely rebuilt one). Napa is all messed up man...

Any master with two reservoirs the same size was designed for 4-drum cars, but you can rebuild them to work with discs up front by removing the residual pressure valve inside. Some early disc cars seem to have an all drum master cylinder built this way. Personally I don't like them because you need the larger reservoir, as found in the later style master cylinders, for the front discs...they can take more fluid. I wouldn't trust one with two small reservoirs like yours.

Tom Condran's book "Performance Handling for Classic Mopars" talks all about master cylinders and bore size, etc. I suggest you read it. There's some important stuff about bore size and how to secure the pushrod and stuff.....Actually, here are some scans of the relevant pages I once posted for someone else.

http://www.enbcom.com/cuda/tech/tom_condran