I received the set of Pixel 7 Pro power and volume buttons from that eBay seller today. As best as I can tell, both the power button and the volume buttons appear to be the same length as those on my Pixel 6 Pro. They seem to be slightly narrower, but I don't think that will be a problem. It appears that there was a mistake in packaging because the volume button is gold, which is correct for my Sorta Sunny color, but the power button is silver. Again, not a big problem.
However, since my power button has only fallen off twice, and it seems to be holding up for quite a while now, I decided not to install it until/unless it falls off again by itself. I'm afraid of wear on the inner plastic tabs by forcibly removing the button. So, although I can't confirm for certain that these replacements will fit properly, it looks promising.