Thanks for your advice thus far Nova!
The gearset I have is for v2 / v3 gearboxes, and that's the gearset that a G&G M14 uses, I'm 100% confident on that one.
I intend to get a new cylinder head and piston head too, I just need to find out what versions to get, should know by tomorrow.
I'll look into the cut off lever, but obviously it'll be different for a G&G M14 so I'll have to dig one out.
What exactly does a cut off lever do anyway, just so I know?