The Slant is a very temperamental little critter. It WILL see the difference in weight and rotating mass going to an 8.75.
Automatic trans? No Stick? Not spraying 150 horse at the hit? KEEP the 7.25!
3.23 and 3:55 were popular gear sets in early cars, as were Sure Grip units. A little hunting will get you hooked up with a killer 7.25 for less than an ABody 8.75 housing will cost. If you're on a real budget, weld up the spiders and have at it.
Spider gears aside, that rear is MUCH stronger than people give it credit for.