This approach was reported in another Forum post several years ago though the person hand laid his dual gauge track. I can't remember the details.
These search results will help.
https://ogrforum.ogaugerr.com/...agination.sort=SCORE
Your center rail will need to be offset a few hundreds of an inch to accommodate the 30" inside spacing. It won't effect the performance of your center pickup roller.
I am not aware of any Gargraves "thin" center rail. MTH makes their ScalTrack with a thin center rail.
Jan