My midwest poor boy opinion:
The 68, that guy has probably 6 grand in that car, probably had it for a while(long enough to pull the rotten interior out, lose it or throw it out when he moved, and "work on the paint" and then let rust come back through the primer), looked at recent prices for 68-70 b body cars, rubbed his hands together and said F it and threw it out there for over double what he has in it. That car is a shell. I know b body cars from the era are at a high point right now but to me that is absurd. Looks like it is full of pin holes, floors are probably not savable(you have to look from under side, but the rusty passenger floor tells me it is coming through the bottom) and no picture of the trunk?
The Challenger is lol overpriced, for the midwest. Maybe 2/3 of what he is asking, depending on an in person inspection. However it does look like a lot more of a starting point than the other car. Rubber underside means you will need to scrape to see what is going on, but my experience in the midwest is the rubberized coatings did make a positive difference. Not sure about out west. You can sell the 340 to some rich guy that won't accept a 360 as a substitute or stash it if you want to keep the "numbers matching" thing going, sell the running 360, fix the wires when you pull the entire interior out looking for the mouse nest, and not have to go parts huntng for silly crap like side marker lights, hood trim, and who knows what else that is assuredly missing from the other car. Heck you might find out the no start is because of the chinese accel stuff he put on there.
I am not sure either is a great choice for a driveline transplant, but the Challenger is a lot more car than the other one.
I reserve opinion on body styles as I joined this board when I picked up a 78 Monaco police sedan, so my tastes won't follow the crowd. if I had to pick, based on both value and in my case appearance, I would pick the Challenger.