Quoted: What if it wasn't registered ? Could he register it on a Form 1 ?

No. You cannot register an existing NFA item on anything except a Form 10, which limits future ownership to LE (even SOTs cannot own Form 10 items).

The Welrod would need to be destroyed to BATFE standards (pretty much, that means running it through a chipper) and then pieced back together like a jigsaw puzzle, and welded up again.

Quoted: Quoted: Quoted: What if it wasn't registered ? ... The Welrod would need to be destroyed to BATFE standards (pretty much, that means running it through a chipper) and then pieced back together like a jigsaw puzzle, and welded up again. Would it be possible to destroy just the "suppressor" portion and keep the "gun" portion in tact?  A new silencer could then be made and registered and installed on the gun.

I'm not Tech Branch, but I suspect you would be in very gray legal waters.

On the Welrods I have seen, the receiver is integral to the suppressor tube. The "gray" area would be determining -- to a degree sustainable in criminal court -- where the suppressor tube ends and the receiver begins. I suspect that BATFE would require the entire tube to be the suppressor, and require its destruction.

In addition, TB has ruled in the past that in certain cases -- exactly like this one, IMHO -- a ported barrel can be considered a suppressor part requiring registration in and of itself.

If TB required you to destroy the entire tube and the barrel, that is pretty much destruction of the entire firearm. You could of course salvage the pistol grip and firing mechanism, and build it up anew on either an F1 or F2. I guess that would be easier than fabbing a Welrod from scratch.