Ok, I have one solution - lay the elevated loop of O31 track on the cutoffs and trace them to cut 3" sub-road. Then attach all of those together and support with 2" x 4" cut-offs. I am working on the fitment. The 2 -12" x 48" cut-offs will cover 12 curves. The 24" x 48" cut-off would be ripped to 12". One and half of those cutoffs would handle the elevated straights as a 12" wide piece for the center. The remaining piece would cover the last two curves and the 2 starights for the turn-around loop.
You can close the ends in or leave it all open.
Here is my version of the track plan. The rail joints end at the table edges. The track on those tables stay with it, like a modular system. This is in Lionel O tubular. O72 outer with 6' passing siding, O54 inner and an O31 elevated. That permits separating the four tables.
