actually, REAL m14s are not converted automatics, but were SEMI-AUTO FROM THE FACTORY- there was a plastic bag attached to each m14 by a wire which contained a lever and spring- when the crates arrived at the battalion level,the bags were removed by the unit armourer except for those which were destined to become select fire- those rifles then had the kits installed -and the surplus units were returned to depot and eventually surplussed to the general public via various routes- a few years ago they were like 10 bucks for the bits, but you COULDN'T INSTALL them legally
however, the real m14s from isreal have a DIFFERENT story- their SELECTOR SWITCHES were WELDED SHUT so they couldn't pivot, and the roller bearing was GROUND OFF to completely preclude selective fire, even if you could obtain a kit-as the cfc insisted- these rifles were then "importable" and sold as "normal" hunting rifles- ie NON RESTRICTED
however, the cfc changed its mind, and someone noticed that the us considered the m14 as a MACHINE GUN, ( once a machine gun, always a machine gun according to batf) and that's why the real m14 is PROHIBITED- functionally, it's no different than the m1a