The MTH elevated are 6 1/2". You'll need something to build up the ends for the 1/2" difference.
I used the O31 on the elevated portion to eliminate hiding the lower level train in tunnels on the ends. You have to run a shorter engine and cars on the O31.
I could try to work the lower level middle to curve more to follow the top to create some more scenery space in the center.
Edit: That doesn't work.
The mountain foam may need to carved out a little to make clearance where the two loops almost touch.