Doing a little snooping around, it appears there are possible alternatives if you need a new relay without spending 200 bucks trying to get one, but you need to do a slight amount of work. It looks as if 20334449 relay is the same relay as the 81-88 with the exception of the bracket. The ground on these is normally soldered to the far end of the relay cap that is crimped on, and the ground is via the bolt to a steel part of the body under the kick panel. If you can solder, you can remove the metal cover/cap from both and swap them, and re-solder the ground to the cap and recrimp your existing cap onto the new relay base. BOOM! Bolt it in place and rehook up your wire plugs. The other option is if you can mount it with the existing bracket. I've never tried, but it's behind the kick panel anyway so who's going to see it. It just has to be grounded to metal to work. Or run a ground wire from the cap/bracket to ground somewhere if you mount it to non-metal stuff.
Standard Motor Products (SMP) was a supplier to GM for the relays like this, apparently. Even has the GM p/n stamped into the bracket. Here's a suitable SMP RY60/20334449 relay on fleabay, about 50 bucks:
https://rover.ebay.com/rover/1/711-...0001&campid=5335822911&icep_item=184080793565
GM pickup trucks with PDL in the 70s/80s era have the same relay with a different bracket. Those are also good candidates for swapping caps/brackets if you run across a good one. GM p/n 14056552.
And if you can find an SMP branded one, the actual 81-88 relay 20306055, it's under SMP RY547.
That's it, no more researching this for me.