I would highly recommend against buying a car that is apart. Unless you were present during the dismantling, and can be certain everything is accounted for, I'd bet some things are missing. And if some of the L78 specific stuff is missing, all bets are off. I can't ever remember hearing about one of those stories that had a happy ending. The prices of '68-'72 Novas have risen significantly, but I think the amount of potential buyers who would have the funds necessary to purchase a restored L78 Nova is less than the amount of buyers that would have the funds required to purchase a restored '69 Z/28 with both cars hypothetically being in the same condition. The selling prices might fall pretty closely; the number of interested parties not so much. And I think the savvy buyer who is educated enough to understand the value of a true L78 Nova isn't going to "buck-up' for a car with a questionable drivetrain.
The second car, in my opinion, isn't the worst car in the world to start with in terms of price vs. value. Personally, I like Fathom Green, (and Rallye Green and just about all the "Earth Tones"
and it sounds like there is enough stuff present that could be sold to lower the initial starting point money-wise. The GM cold-air hood, the diamond-tuck interior, etc. are items that could yield some good sale prices and offset some of the cash outlay.
It sounds like neither one of those cars would ever have a true "born with" drivetrain, but with today's terminology they both could be "matching numbers". I wouldn't represent either one as such, but many (including some auction houses) would.
Out of the three cars you presented, (IMO) car #3 seems to have the most potential in terms of money, time, work versus return. Car #3 also sounds like with some TLC it could be turned into a fun "Cruise Night" car in the not-too-distant future. The pieces that are missing are certainly available, in fact you could probably make one call and get everything and not have to settle for aftermarket repros. Car #3 also sounds like it would be very desirable when restored and would sell rather easily. As to whether or not it would make a profit, there are far too many variables we do not know at this time to render a guess. I'd say if that car is relatively rust-free and is what I'm imagining from your brief description, it is probably worth in the $30-$40k neighborhood depending on what else might be missing/present...(bellhousing, shifter, original wheels, etc.)