[kaskillah]

You could get the front disc brakes from a later year Maverick or maybe even a Fairmont. You would need to change the knuckle/spindle assemblies. For the rear, you will probably have to swap a rear end from another Ford product. I have heard you can use the rear end from a Lincoln Versailles because they had disc brakes though I never heard one used on a Maverick.
I had an early model 1970 Maverick in the 80's. It was a bullet-proof car. I couldn't kill it. The drum brakes on the rear end are more than adequate. The front brakes sucked because anytime you would run through a deep puddle you can lose them unless you applied the brakes when going through it.
Honestly, I don't think it's worth the trouble to make the change unless you were also thinking about dropping a V8 in it.