I just put one of these on my NU50.
https://www.treatland.tv/OMG-honda-motorcycle-petcock-16mm-x-1-5mm-p/omg-16mm-01z3264267.htm
Bolts up perfect, you'll need a reducer for the fuel line because the output fitting is 8mm instead of 5mm. Also the line fitting comes out the back instead of the side, no big deal for me. Turn it sideways or loop the hose around.