Another 8.75 post

What you bought is a 64-earlier B body rear end. The Castle but is a dead giveaway. As RRR said you’ll need to chop those ends off and use the 65-up axle ends, and use new/replacement axles in whatever flavor you prefer (A SBP/LBP), replacement backing plates and drums. It might be less expensive to find an A Body 8.75, although I see they can be pretty pricey