IIRC, the MG42 was reincarnated as the MG3 by the Germans. The original plans had been lost in the war, so they had to reverse-engineer plans from existing WWII weapons.
I think the main difference in MG3 was that it was chambered in 7.62 nato, and some other minor differences.
ed: what does the M60 have in common with the mg3 and mg42, lasersailor? The M60 is gas operated, while the MG42 is recoil/gas operated. The MG42 doesn't even have a piston for its gas, just the deflector near the muzzle.