"...THE FIREWALL AND DASH RETAINING THE M-CODE ID WERE CAREFULLY INSTALLED ON THE TEXAS DONER CAR AS WELL AS ALL OTHER IDENTIFYING MARKS..."
Besides the obvious fender tag and actual Vin tag jumping, I'd expect the "AS WELL AS ALL OTHER IDENTIFYING MARKS" statement mean he's cut out and welded/transfered whatever amount of the original car to include the hidden Vin locations on the rad support and whatever the rear area location is on the fastbacks (parcel shelf on the notchbacks)?.
As much as the guy's being up front about it now, the disclosure is in hoping it's a way to cover his butt if ever necessary later after passing this car on to the next owner...but what he's done is waaaay beyond any gray areas of rust or collision repair and outright fraud!.
There's better cars to find out there that you can enjoy without fear of the feds knocking on your door someday..
~ Pete