As far as trusting Ebays 'parts compatibly I have seen lately a listing showing a 1955 Chevy front fender as working on a Kaiser, as does a 1951 Ford door. Ebays listings are getting like an old J.C. Whitney catalog, real suspect.
Absolutely. It's been that way for years, unfortunately. I am constantly dealing with the incredible amount of misinformation, ignorance and outright dishonesty from all manner of sellers in the automotive parts world, especially with vintage stuff, double especially with online sellers with almost no accountability. Just last week, I was trying to source some seals and such for a '62 Ford Ranchero with a Fordomatic two speed. O'reilly claimed to be able to get some of them, but when I made a comparison with the ones in the transmission, they were totally different. Their computer had a completely different transmission listed for that car than what they actually came with. The kid behind the counter didn't have a clue of course, had no idea what the difference was. That is unfortunately par for the course in the mainstream auto parts world now. If they can look it up easily for a common vehicle, you may get the right parts. If you have something uncommon or totally out of the mainstream, you're going to get a lot of blank stares.
Thankfully Trans Pac had a complete seal kit for me, for a reasonable price. That's what I worked on today.