I recently bought a remanufactured Master Cylinder and I have been looking online and notice a visible difference in the 64-72 Master Cylinders and was curious if someone could tell me the difference between the two if any. I am assuming it if just who they were originally manufactured by but do not want to assume anything.

 

Manufacturer
Power vs. Manual Brakes
Model Differences

 

The LH picture was used on the 67-69 disk brake cars and the RH was used on 1970-72. There are also many aftermarket replacement units that look different but are functionally interchangeable. All that matters functionally is the bore and stroke of the cylinder. The outer casting shape and reservoir shape only matters if you care about appearance.