Well I got the new GM catch yesterday, and made a first attempt at replacing it. It fit in the trunk lid ok, and the key lock and solenoid operated just fine. But wow, I didn't realize how badly the geometry in the rear of my car was messed up by that long-ago accident until I tried to get things lined up. It looks like the body shop had manually bent the old striker (with a sledgehammer?) sideways to get it to catch. There are large holes in the new catch to allow for adjusting the mounting bolt position, but they weren't big enough so I had to drill them out a little. I finally got the catch and striker to line up and open/close ok, but now the trunk lid doesn't line up with the rear fenders. The striker isn't adjustable, I think that next I may drill out those holes to move it down a little. Or modify the catch bolt holes more. The rear of the trunk lid is still more than 1/8 inch too high. Which of course looks bad, but also doesn't snug the trunk lid against the trunk seal as well as it should. I suppose I should put a new trunk seal in there too, although the old one still looks fine, a new one is probably thicker and would hold the trunk lid tighter.
Anyway, it doesn't rattle as much as it did before (there are still 4,352 other things rattling in the old girl when I hit a bump, that w-body chassis does NOT like the top cut off) so I consider it a win. I'll do some more adjustments when I get a chance. Thanks for your help with the part numbers, Jiggity76!!