I have a N15 tank on my '67 P11. Basically the same as a G15 tank. One thing I don't like about the version of N15 tank I have is I can't use the nicer alloy fuel cap that screws down on two pins either side inside the fuel filler hole. Those pins are not part of the design on my version of N15 tank, and I have to use one of the chrome after market wedge-in style caps. If I fill the tank close to the top, fuel finds its way out on hard braking until the fuel gets lower in the tank. This happens because the seal isn't pulled down tight on the top of the fuel filler hole, like it would (might) be with a screw down cap. At least that's what I tell myself.
I'd look for a fuel tank that could use the alloy screw down cap, if I was looking for a tank again. The chrome cap looks like it was made where it was made. The alloy fuel caps are probably made in the same place, but they look better to me.