I can tell you something to be real aware of and that's the body differences between Chevelles around the rear window and rear deck.
I've got a '67 300 sedan; I'm not sure if the differences I'm pointing out relate to whether the car is a coupe or a sedan or just native to the 300 model, but the rear window & moldings (possibly), lower rear window channel panel (definately), trunk lid (possibly) and tail lights (definately) are all different on a 300 sedan as opposed to a coupe.
I found this out the hard way; my rear window had lots of rust in the lower channel--so I ordered a repro panel that forms the channel for the window and the weatherstrip channel for the trunk lid.
The order guy never asked whether I had a coupe or sedan--and of course the panel wasn't even close. As it turns out, you can't get a repro panel for a 300 sedan--at least I couldn't find one, and I tried many places, including Year One's secret suppliers that they told me about.
Bone yards claimed to have the piece, but let's face it, it's so prone to rust, I figured what are the chances of getting a good one--and they wanted about $300 for one.
Anyway, that's no small problem if you have lots of rust in that area. I welded the crap out of mine, used epoxy putty, POR15 etc., and can only hope it is water tight, as it is the main source for water in the trunk, which rusted the trunk panels and lower quarter panels--so getting it fixed is pretty key.
And it made me wonder whether the rear glass was the same or if it too is different. I've seen lots of repro glass ads for rear glass, but now I wonder if they include the sedan, given the differences in channel shape I noted when I put the coupe channel in place.
I also had to replace the front pilar covers that form the verticals around the windshield--these I got no problem from a bone yard, but there was a lot of back and forth about whether it was a coupe/sedan--at first they picked those from a coupe, and before sending it realized the mistake and had to go back and find sedan parts.
