I have a 71 Cuda that had a NOS 70 fender installed with a plate welded in with the gills. I eventually got a NOS 71 fender that I installed on the car. I remember vaguely a little work was done to fit in the 71 headlight bracket, but that was about 40 years ago.
Start with the dimmer switch. Being some 50 years old they are junk to begin with. The thin wiper arm breaks off and that is usually the problem with it.
You mention needs plugs. If plugs were removed make sure you can turn over engine. A friend of mine sold me his 340 Dart and had removed the plugs and engine was solid frozen. I had to bang each piston with a rubber mallet to get it apart. The other thing if it was a racer may have high gears in...
Never liked the round tail lights on any of the 60's cars. But that's my opinion. When looking for a car in early 80's had to be 70 or 71 Cuda. Settled on a 71, because not a lot of choices back then.
How good a piece are you looking for? I have one and if it doesn't have to be perfect I can dig it out tomorow and take a picture. I know its not perfect but it came off a 70 Dart 340.
The biggest problem when the heater core is good is trying to remove the hoses. Trying to twist them off will sure cause a problem. I recently removed hoses on an old honda van but used a thin pick between the hose and the receiving mount metal and all came off easily. I did ruin my heater core...
I remember some kind of problem with the outside handle getting disconnected from the rod that operates the opening mechanism. If the door is locked and you force the outside handle something on the handle breaks disconnecting the rod. Hopefully you can open from the inside and see the problem...