A Point I would make.
O-31 is 31" from center rail to center rail. The outside edge of the track is a couple inches larger.
I would make the table 36"X 54" minimum for an O-31 oval w 20" of straight on each side. This gives you a couple inches outside the track all around.
For the version with easements will just fit on a 36" X 60" table but have barely an inch all around.