code 80 is SetTrack and code 55 is StreamLine track, the code is the height of the rail above the cross tie, The larger the number the taller the rail is, i.e. Code 55 rail = .0.55 inches
Most N scale track is code 80
Also you can mix Peco and Arnold track just by cutting a few sleepers of, worth knowing if you can find a good deal on ebay or somewhere like that
Hope this helps?