I know this will make me look stupid, but…
I had a '77 Chevy pickup and the front brakes were hard. They also dragged a bit. I spent several weekends trying to solve the problem. I drained and bled the fluid, replaced the master cylinder, removed and rebuilt the wheel cylinders, and even replaced the brake proportioning valve. The weird part was that both wheels behaved identically, so I assumed the problem was somewhere in the system common to both front wheels.
By accident, I found out that the rubber hoses to the wheel cylinders were partially clogged. It just so happened that both of them were clogged about the same. After all the time and money, all I had to do was remove them, run a wire through them, blow them out with compressed air, and reinstall them. Along the way, I damaged the radiator while removing the proportioning valve, so I also had to remove the radiator and take it in for repair. I must have spent $350 and 10 hours trying to fix the problem.