My memory of the insides of the genuine style m/cyl (incoming fluid enters at the end, output at an angle) is the piston has a rod and spring clipped in its end, with a small valve on the rod end to close the input hole when piston is pressed.
MMMMM. My clutch master has its feed from the reservoir going in the same connection (hole on flat at end) as the brake master, and pressure output out the angled connection. I think that means the interior is the same structure.
Here is my spare, ready to fit when I do the LT77.