Residual Pressure Valve placement

Quick "hillbilly" way to check.
Put a small amount of brake fluid (silicone brake fluid) in the front (small) reservoir. If it does not leak out on its own it has a check valve in it.
As I said "shade tree" test, but it works.
You can not have a residual valve on disc brakes cause they would not release.
No return springs, just the square cut seal.

For a rule of thumb, if a master cylinder has two small reservoirs it is a drum-drum.
If it has one large and one small it is a disc-drum cylinder. Large for disc.
I really did not want to post this but I will.