The fire control parts do not make it full auto or illegal, the reciever is what is going to be in question. If it truely is an M1 receiver that was converted to an M2 then yes the receiver is illegal as it was made into a machine gun. You have to machine 2 places on the receiver to make it auto, so that shows intent which is illegal in of itself even with out the parts.
Just like an AR with the auto sear pin hole drilled. That is considered a machinegun even with out anything else or any part in the receiver, the same goes with the M1 to M2 conversion.