The ad gives me pause; wonder if he knew what he was doing.
Yep, you can convert a SBS, SBR, or AOW from a Title II NFA firearm to a Title I regular long gun and ask to have it removed from the NFA registry.
But once a machinegun, always a machinegun.
People did convert open bolt semi-auto Spitfire carbines to full auto on a Form 1, but that window was slammed shut May 1986.
There are a few full-auto Reising 50s converted to semi-auto Reising 60s with ATF blessing in the 1950s but that was a special case.
My attempts to link to the ads returns the Florida page with the note: "Not enough information to display the listing. This may be due to the listing's expiration."