so the gm bumpstops for the rear are generally low quality (in my opinion) and pricey at $20+ each. one of mine is heavily split (maybe repairable with spray foam??). they are attached by just slipping in with the spring seats and merely held in by the force of the spring at the top side of the spring. in other words there are no fasteners...
i have a pair of these nice polyurethane bumpstops by Energy laying around https://www.energysuspensionparts.com/9.9101 i got em from a bargain bin, only 55cents. only problem is, i dont remember seeing a good way to attach them on the top side... there is a nice spot on the bottom side where the oem bump stops hit. that looks like a prime spot to drill&tap&loctite... i dont believe there was a way to get under there to get a nut on it so definitely loctite... but the question is: can bumpstops go on the bottom, attached to the axle assembly?? bc i generally only see them on top where the OEM ones are...

the oem ones are almost like a hollow foam-ish piece, i think you -could- tape it up at the bottom and anywhere it is split and just shoot spray foam in there and let it dry 24hr+ then remove the tape. it would probably be -about- as good as a new OEM one and save $40 bucks