I somehow missed some of these posts, and just saw them now. I emailed the guy with the craigslist ad, and I’m watching the eBay listing. Neither of those are 78 seat, but I think the seat pan is correct. Not sure if the one on craigslist is metal or not, so I asked him about it. If I can’t find a real 78 seat then using a 77 seat until I wear the cover out is good enough, and then I can just get it recovered with the correct pattern.
If all else fails, that other website had a metal seat pan down at the bottom of the page. Thanks guys!