John,
There are a number of tracks that accommodate both 7-1/4" and 7-1/2" gauges. While guard rails can be a problem, spring loaded guard rails and wide flangeways can take care of that. The main problem is on curves, where many widen the gauge on curves, allowing the 7-1/4" gauge wheels to drop inside the rails because the check gauge is too wide. Those tracks that allow both gauges have very wide radius curves, and they can hold the gauge to exactly 7-1/2".
The late Dr. John Brace of Cherryfield, Maine had a track that would accommodate both gauges.
Keith