Comments not withstanding, here's what 2 concentric O72 ovals would look like.
The track is Atlas.
The White crossovers are 45.5" wide to represent the bridge. Since I don't know more about the bench work, I placed one on each straight.
The center-to-center track clearance for the crossovers and straights is 4.5". The crossovers maintain the center-to-center clearance around the layout during the design phase.
The Green rectangle is about 6.65" wide and I don't know if 2 tracks will fit on the bridge.
The Yellow rectangles are 3" wide to show center rail distance to wall or edge of layout. As you can see, it would be close on the bottom if the bridge is placed on the left or right side of the layout, though you do gain 1/2" because the bridge is only 45", not 45.5".
If there is an aisle into the center, a lot can be done to add sidings, etc., so this is not intended to be a suggested design. Its merely to show the space.
