What is the difference between these two master cylinders? Dorman M75817 and M75818.
Per the summit page M75817 is for manual brakes and
M75818 is for power brakes. Or at least it is the correct part if you have a pdb b- or e-body. 817 is listed for disc brake cars only if they are manuals (a-bodies).

From the outside they look the same, the piston diameter is 1.031 on both, and also both have reservoirs for disc brakes. So where is the difference? Can I use M75817 on a power disc car (1971 Super Bee in my case)?