[twertsy]

I do not believe there is any welding done on the block re-stamps. They just grind them enough to remove the existing numbers and re-stamp the new machined surface.
Does that machine work to show prior stampings below the grinded surface. I assume the metal molecules are somewhat crushed deeper into the metal when it is stamped..?? I once contacted a 'scientist' about a ZL-1 block who mentioned about 'etching' the metal??

I'm not familiar with "etching." Unless he was talking about them using etching to fake the stamp/numbers. In which case, that could also be detected.

So, several things: first, if the above is their process, I would think precise measurements would reveal that process, given known blocks were from the same mold. Second, if measurements aren't reliable, infra-red would be very likely to reveal remnants of the original stamp underneath the fake. Lastly, if you had a thermal infra-red image of a known real block (after heating), then compared that image to the one in question (again, after heating), you would see anomalies in the "worked" area. You MUST image them from the exact same angle however.