Maybe this is old news, but I've fixed my mushy brakes by adjusting my drums. I bled the brakes thinking it would fix it and it didn't, so my friend suggested to adjust the drums so that the shoes are closer to the drum itself. That fixed my spongy pedal feel. Very easy, you don't even need to remove the drums to fix this, but I did as you have better access to the parts that need to be fiddled with. How to adjust a drum brake is easily found using the search function.

Just thought i would share, this made my day.