Switching from 8-1/4" to 8-3/4" rear ?

To go from an 8.25 to an 8.75 you will need replacement SBP wheels (unless the 8.75 has replacement LBP axles in it). You can reuse the shock plates and might be able to reuse the U Bolts (but I would probably use new). You might be able to reuse the brake hose but again, I would replace it. You might be able to reuse the rear U Joint depending on what's on the 8.75 pumpkin. Check the oil level in the 8.75 after installation.