As for the tank, the fact that the overspray is on top of the Zeibart makes it impossible for it to have been factory overspray. Also, the fuel tanks were not in the car when the body was painted. The straps themselves were in the car and hanging which results in an odd factory situation where you'd have body colored painted straps and a natural metal tank. Could it be similar colored road dust and not orange overspray??? I would ask the seller to get you some natural light photos (no flash) of the sides of the gas tank to see what we are looking at.
Is there a way anyone can get a photo of the underside edge of fender edge by those cowl areas? If it's black under there then the orange is later overspray. If its orange under there, then it could be factory applied but with a really skimpy blackout treatment. A plus is that there is no orange paint on the cowl seal and the green zinc is fully intact on the retaining clips (the zinc finish is easy to damage when removing these clips)
Maybe we can get fellow member 70copo to render an opinion on the paint process as to whether the blackout paint occurred before or after body color was applied. He literally wrote the book on the Norwood Assembly plant and its processes.
https://www.norwoodassemblyplant.com/ (i'll send him a message)
BTW, in the ad they indicate:
"the heating and fan control has been disconnected, as the original owner removed the heater core from the car in 1990 when it was set up for long-term storage. The original heater core IS included, and with it installed and the fan controls connected again, I am quite sure it would function."
When you look at the engine bay you can see that the heater core nipples are showing in their original place sticking out of the firewall. Just the hoses appear to be missing. It is a major job to do a heater core on one of these cars. Like 8 hours labor. (in the thread on my 73 you can see how involved it is. To do it right, you have to pull the bottom bolts out of the fender and inner fender to access some of the heater box bolts and the heater box comes out from the inside of the car after you remove the seats, console, radio, all the skin from your knuckles...)
All in all it looks like a really neat car and I think you'd have a lot of fun with it, though it only has around 185 horsepower. The underside cleaning would be fun winter project in a nice heated garage. :-)