"proper code of rail for On30 " The answer is YES! 
If the narrow gauge line is a stand alone out in the woods line it could be very light rail. If the NG line on the other hand has an interchange with a common carrier railroad then in that interchange area the rails would necessarily have to match. Depending on the railroad things like bridge rails or dock rails may be different than the regular NG main. So the correct answer is really - IT DEPENDS!
We are modeling Chama to Antonito summer of 1940, all of the rail is code 83 EXCEPT in Antonito which is code 100 and the hidden staging which is also code 100 (cheaper). Russ
