In the below photo you can see me using the tried and true method of using white glue (actually, I used carpenter's / wood glue version of white glue just because it was handy) and pins to hold the track in place. I wasn't sure how the ends of the track were going to work, but with the help of my Dremel was able to get a nice even cut of the track to match the front of the diorama:
Below is the cork roadbed applied for the second level, a Kato two-track girder bridge, and another section of unused Kato double-track that I will convert to another bridge:
From the other side, I am thinking of adding a road bridge over the tracks on the other end of the diorama to add more depth and dimension to the diorama. I'm intentionally trying to make this diorama as 'busy' as I can make it!