I'm looking at a drawing of a Pere Marquette 50' gondola with wood flooring. It's "2 3/4" x 4 15/16" Shiplap". In HO, 4 15/16" is .057". The matches are also awfully thick, though in a gon, that wouldn't show.
Tough one.
Ed
I don't think this is something to agonize over. I have a Tangent gon and it looks like the "floor" boards are around 4 inches wide. I have a LifeLike P2K gon and the floor boards are around 6 inches wide. These are not accurate scale measurements, just a close eyeball. Anyway, both look acceptable to me.
Matter of fact, if you have any gons with the floors already scribed in them from the factory, that will give you a guide as to what to make your own board widths.