Just had a look in one of our old Mitchell manuals here at work and this would definitely be from a '75 - '80 with the leaf spring suspension and the possibilities that it shows it came with are 8", 8.7" and 9". Hmmmmm....I had never actually heard of an 8.7" before but seeing as how this one has a pan on the back it would have to be that one...odd! Definitely is not an 8" or a 9" though, they are the pumpkin style. I would stay away from this one due to the oddity of it.
I've got one just like that under a 77 Granada parts car, it came with a 351W C4 combo, I thought the car would have had an 8" or 9" in it I could use. The motor I used in my 84 pickup, the tranny and disc brake setup are going on the Comet. I don't know if 8.8 parts will fit or not, probably not worth much more than scrap iron, but I could be wrong.................
