Pete, I added a second drawing to your photo album showing where you could put double-insulated gaps.
For the lower layout, (which is basically a loop), double-gap as shown by the four 'X's.
For the upper layout, double gap at the four locations as shown by the 'X's.
That will give you a reverse loop (A thru B to C and back to A) long enough for roughly a 125" long train.
Also in the other direction, D to C to B and back to D.
Just one way to do it. Paul O