whats the difference between the older 50rv and the newer 50ng got what i think is a decent deal on a 50rv nib and would like to know about the engine

50NG(Next Generation) is redesigned with hidden transfer ports, lightened piston and different exhaust port timing.
Thanks,

one more question . are the prop holes the same on the rv as the ng (do they use the same jig) i have to get a spinner cut and i need this info

thanks in advance
john