Surprisingly hard to get info on Neal Smith M14s other than they might have actually been welded together by someone else and just have his name on them. I was wondering what the general opinion is on them? Issues with the rewelded ones, could they be trouble like rewelded Thompsons?

I can't help regarding Neal Smith, but I would get it X-ray inspected before spending transferable MG money.
If it was cut & welded way aft of the bolt lugs, it's unlikely the affected heat treatment will cause failure. Voids would then be the most likely mode of failure.

If it was ever cut near the locking lug area, I wouldn't buy it.

Isn’t Neal still alive? You could look him up and ask him.

Next best option is to post on Subguns and the Machinegun Boards.

He is still alive and according to machinegunboards he does not do the whole internet thing and would have to meet up with him at special events like the Knob Creek Shoot.  That is where I read he may not have been the actual maker of some of these.

One has a cut behind charging handle so lower mid section of the bolt and another is at the rear end of the receiver just under the rear sight.  The first one I have been told has been checked out.  I live in the middle of nowhere really and do not have access to or connections to anyone that check and make sure and would most likely have to take their word for it, though they have a great reputation and do trust them.

Find a place that does non destructive testing for airplane parts.