It’s a ‘69 Barracuda. Original 318 2bbl replaced with a mild rebuilt ‘70 340, 904 console, 3.55 Imp rearend. You may be right that’s it’s 9 1/4, I’ll check again, but what I’ve found online indicates it’s 8 3/4 and 74-75 were the only years with rear disc. It’s an unusual design with 1 caliper leading the axle and 1 trailing - came that way from the factory.