The differences aren't enough to not work. I'm running a '96 Subaru Legacy master that's operating GM metric discs and drums. I'm sure the Subaru brake are quite different, but it works great. I did add a proportioning valve at the rear brakes.
Just find a master and booster that is readily available and whichever you prefer, Ford or Chevy. You may want to take your's to a wrecking yard and compare the physical size to master/boosters until you find one that looks close, then go get a new setup at the parts store once you know a make, model, and year. That's how I ended up with the Subaru setup, but I took it off the car along with pedal assembly, and got master, booster, and pedal assembly for $50 total.