You can purchase another rear end out of another full size car but when they changed the rear end to make them stronger they changed the brackets that mount the rear end. So you will have to carefully grind off your old brackets and reweld them onto your car.
The factory not only changed how the rear end bolted into the car they offered two different rear ends. They continued to offer a ten bolt 8.2 inch ring gear for those cars equipped with six cylinders and small V-8's under 300 horse power, and a bigger 8-7/8th inch diameter ring gear 12 bolt for cars with a 348-409 (396) and hot 327's. When they switched over to the Salisusbury rear end they lost the ability to have a single differential carrier fit all of the gear sets they offered (as the gear ratio changes from a low number such as a 2.56:1 to the highest 6.13:1 the pinion gets smaller in diameter as it looses teeth and the ring gear gets thicker as it gains teeth). Your Hotchkiss style differential is able to slide back and forth inside the differential case using two spanner nuts to center the ring gear on the pinion. The new Salisbury rear ends made by the Spicer division of Dana-Spicer uses three different differentials that fit inside the rear end. Each differential has a flange to mount a ring gear sub set of the full range of possible gear ratios so it narrows your gear choice.
The factory used mostly a three series gear in most cars (3.07:1 being the most frequently used) but offered a two series of gears in six cylinder cars for those interested in economy (because a six often has more than a similar sized V-8). But for trucks and cars that tow trailers they offered a four series of gears favored by performance enthusiasts. So you have to determine the gear in the case before you buy the rear end based upon the gear you want and be happy with that range limitation.
Finally in 1972 the factory only made one Salisbury rear end offered on all cars and light trucks (the corporate rear end) that has an 8.5 inch ring gear. It comes in two flavors a two series rear which is most common in older cars and a three series carrier that is found behind most cars with an overdrive rea end to improver performance without harming mileage. You will most likely find an 8.5 rear end under cars in the salvage yard now.