New to mechanics - advice welcome

LOL. You're askin the wrong crowd for advice on buying a GM

GTO and GTX will normally cost you more simply for collectability compared to a Caprice. You can "fix" that by scaling your choice down from a GTO to a Lemans, or a GTX to a Belvedere hard top.

Parts are likely to be more available and cheaper for a Chev, but frankly, I thought the design of the 67 Chevs were a complete dog. On the other hand I always thought the 67 GTO was pretty nice, design wise, along with any of the 67 Mopars. But if you are gonna go GM you might consider Chevelle, which is pretty much the same platform, comparably, as a GTO/ Lemans. So there you have it --personal preferences immediately surface.

But just about any of these cars are "what you make of them" as well as "what you start with." If you start with a rust bucket and bondo it together, that's what you'll have.