How do I find an 8 3/4 rear in the jy

Last year for 8 3/4 is 1972 (73 and up 8 1/4 was the "heavy duty" rear - bolt on rear cover w/ 10 bolts)
Any car could be ordered with a 8 3/4. My 1970 Swinger with a 318 2bbl came with one, god knows why since I bought it from the original owner in 1983 when she was 86.
In 1972, since it was the last year for them, they dumped a lot of 8 3/4 rears that were at the factory in what ever they were building at the time. They knew they would continue the 7 1/4 for many more years. I've seen 8 3/4s on 318 and slant 6 cars and even bought a few dead 4 doors just on the value of the 8 3/4 rear.