Rear Brake Drum Screws

[mytruck1949]

Gang
Total newbie here with these trucks but enjoy working on them. I currently have a 49 chevy 3600. This weekend i started working on the brakes. First had to knock off the mud off the rear drums. Next in trying to get the drum off, which isn't budging. I see that their are 2 flat head screws. Logic tells me these screws hold the drum to the axle but don't want to go off and break stuff. If so tricks to get these broke free. I am soaking them in PB blaster.

Also the brakes are not locked up so i can spin the axles.

So what are these recessed flat screws?