STD 72 on the main level with five rail STD/O 42 on the upper level. My Standard Gauge AF cars run fine on it. I don't have the extra long AF cars though, but my Ives cars run fine on STD 42. I double head my 400e's and have them coupled. Double headed, they will only run on STD 72. They swing of the front end of the 400e will pull the tender of the other engine off the track on STD 42.
I run tubular rail now. I got rid of the standard gauge MTH plastic roadbed track.
George
