Andy, I'm glad you and your sons are having fun with this. I'm sure whatever you all come up with will be great, and like you say, it doesn't have to be permanent.
Adding to @RSJB18's comment, but maybe too big for this layout, here's a FasTrack Reversing Wye using O72 minimum Curves and no cut pieces of track drawn in SCARM. Note the short pieces in blue are 1 3/4" and all others are the 1 3/8" Half-roadbed that come with O-72 FasTrack Switches. Just something to think about.
Good Luck!