Hi Tom,
First problem is MTH RealTrax has O-42 curves, not O-45.
Second problem is CAD drawings don't always match real tracks.
Third problem is because RealTrax has limited fitter pieces making it difficult to make the loops concentric without cutting tracks to fit.
Here's a SCARM rendering of what it would look like with RealTrax O-54 outside and O-42 inside curves. Note I added crossovers so trains can run on both lines. Also note the green tracks should really be O-54 to make the loops concentric, but you'd have to cut RealTrax straights to make things fit. As it is, there are 3 places where the tracks don't join in the software, but I believe they'll join when built.
I've attached a photo so folks can see what we're talking about without opening the PDF and a SCARM file for others who might want to play with the design. I didn't take time to refine the design, just enough to show you what it would look like with actual tracks. Hopefully I didn't make any mistakes, it's only 7:00 here. 
