brake blunder :-(

The front part of my car's master cylinder is draining very slowly, but enough that I suspect a leak. I was checking the wheel cylinders, in case I saw the leak, but stepped on the brake pedal without putting the drums back on first! Obviously, impossible to put them back, how to be able to replace them? The brakes are complex with a lot of very strong springs.

Did you try to open the bleeder on the back plate to relieve the pressure and set the pads in place and close bleeder.