Some other hints for removing the drum retaining screws:

I gave up on impact hammers, as I always break/twist the bits.

I lube thoroughly with penetrating oil, then I use a chisel and a hammer to try and turn the screw.

If that doesn't work on it's own, I take a drill and a 3/8" bit and drill into the center of the screw. After I make a hole approx 3/8" deep, I use the chisel again. By removing the material in the center of the screw, it allows the remainder to flex and a few whacks with the chisel and they turn out.

Successful 9 out of 9 on this truck.

My brake lines screwed right in as well.