Never heard about M-60s, not surprised though, same criminal operation maybe?
I knew there was AR-15 LLs made into RDIAS, the HK sears/packs (replacing) the trashed RR debacle, a few rare bits of "monkey business" in this whole hobby. Yrs ago we heard of the M-10/11 serial numbers being added to "new" MGs, there was heated talk of it, even rumors one GA manufacturer did indeed paper Thompsons/1919s as M-10/11 numbers back in pre-May '86, didn't see how NFA gang would let that slide, life has taught me that ANYTHING is possible.
Guess a lot of buyers were somewhat confused with examples like DLO, registered tubes being used to build other type "tube" receivers, all legal per FTB. Combine that with the fact ATF once allowed original manufacturers to replace damaged MG receivers, doesn't take rocket scientist to see the train wreck ahead. Perhaps someone got the bright idea to add registered MG parts/serial info to build new MGs, and here we are yrs later, pass the Kool-Aid.
This whole thing has blown wide open, the tax man comes calling, as ATF reviews registry, there's going to be a sh*tload of unhappy campers. Always Think Forfeiture.