I'm thinking that you will need a specially built rear end housing/axles to fit that small chassis Ranchero if you feel that a 9" will be needed for engine horsepower. An 8" or a later 8.8 might be a better fit if you are looking at not spending the kind of money a special jousing costs. An 8" is good for at least 450Hp and can be found in some Pintos (wagons for sure) and about anything else Ford built with a 302 or smaller V8 as well as a lot of the I6's. The 8.8 - Mustangs from at least '86 and possibly a bit before, is good for at least 500hp and many have disc brakes and an integral e-brake in the rotor hat. I have a '57, the narrowest 9" in my '31 and have to say it could have been an inch or so less wide as my tires are just barely (legally!) inside the rear fenders.