1980 Pantera GTS 4 S ??

In my opinion this is a GT5 just like you said, and someone is trying to represent it as something it isn't. Which is pretty stupid cause just being a GT5 should be enough on it's own. It is not built as a race car. It has a full interior, bumpers and it probably weighs the same as any GT5. I don't think DeTomaso had a factory race team after they got involved with Fors, which is part of the reason are cars are worth even more money. I mean even the guys that raced back in the day, Detomaso just sold them a car and said "Here ya go, good luck" and that was about all the support they got. So if you are looking for a true one off race car that ain't it.
There is however, a real, true authentic one off DeTomaso race car for sale right now and some lucky guy is gonna get it. It is called an XP70 and it is gorgeous. It is a Can Am car that was never completed. The owner, some Texan named Carrol Shelby, stiffed DeTomaso on the car and backed out of the deal. Now its for sale.

I believe this is the real deal, I am curious about the chassis number. I would expect a 1980 car to have an Embo series chassis number. I always supposed the GT4s, if any existed, would have Vignale series chassis numbers. But we live and learn, eh Peter.

The original six GT4 cars were built along with the Group 4 race cars, and some of those were pressed into service in the World Endurance Racing Series. Later GT4 models were supposed to be GTS models modified with bits and pieces from the Group 4 race car. I am beginning to understand that the GT5 evolved from the GT4. I have read that factory documents describe GT4s as modified GTS models, like an upgrade in trim, rather than a true separate model. I doubt there are many GT4s in the world, talk about a rare and desirable Pantera!

My guess, this is an early GT5 in which the factory was still using the GT4 description. Its rather obvious that GT5 assembly began before the official introduction in 1980.

And so our knowledge grows with each new discovery.

cowboy from hell

I think that just the skins on the doors, hood and trunk are aluminum. The shells are steel.
I went through that 20 years ago with Hall. There were no lightweight shells. Only steel.

For about $10,000 worth of skins, you could save 100 pounds on the car.