Actually...
If you use N-scale mechanisms and track, you will have HOn30 (HOn2.5, HOn2 1/2, or whatever you want to call it....)
Some might even argue HOn2...
N-gauge track is 9mm...
HOn3-gauge track is 10mm...
So, if a rivit counter were to attack, you'd want to have a set of rubber calipers handy to fool him with...
If you want HOn3, use the N-gauge track and mechanisms. It'll be our little secret... :thumb:
The general rule of thumb is the same as using HO gauge track and mechanisms for On30.
For the track, bury the ties in ballast, muck, weeds and grass to hide them. Or remove every other one to give the track a narrow gauge look.
For the mechanisms. You can buy kits to bash the N-scale equipment into HOn3. Or do a little scratch-building and kit-bashing.
This usually means putting on a larger cab and details...
Good luck and have fun...