It seems that Bill may be thinking that a narrow gauge loco needs different track..
I suggest you start here: in G scale, as different from other scales... the track stays the same, and people use different scales on the same track. This is typical (there are variations). So using 45mm track for standard gauge, you wind up running 1:32 to be accurate.... if you us 45mm track for narrow gauge, your scale winds up being 1:20.3. There are other scales applied to 45mm track, but these 2 combinations are the most accurate common ones.
So if you walk into a hobby shop and buy a Bachmann K27, which is a model of a narrow gauge mikado, you get something that runs on 45mm track but is scaled 1:20.3... now go into another hobby shop and buy an MTH Hudson, it will run on 45mm gauge track, but it's a standard gauge loco, and the scale is 1:32.
Very weird if you are coming from another scale, hence, my guess at your confusion.
I hope that helps.
Greg