To me, there is no debate. This is as the attorneys say, "a paper case", in that we are looking at documentation from the manufacturer and it is up to the contraries to prove the documentation is not accurate.
It is a Ford production discussion. Not a Pantera production discussion. With Panteras there simply is no way to accurately document what engines were installed new in the Panteras.
Considering that there is NO authority to judge originality on Panteras, unlike Mustangs, that may be a stillborn situation anyway and not matter much anytime soon?
Anyone thinking investing in "original" Panteras, whatever those are, is likely very ill advised to begin with and there is no sign that will ever change in the future.
Claiming originality on a Pantera is just a salesman's ploy of throwing enough crap at the wall in hopes something will stick.