8.25 rear....1985 sure grip swap into a 1973 housing?

The pinion depth shim is gauged off the housing. The gears may have a variance from zero number on the pinion. A factory service manual will chart that can help you decipher a shim change if needed. The easiest way to start is to use the shim that came set from the factory move it to your new gearset and see how the contact pattern looks