I reached a milestone yesterday - the mainline is now complete (well, except for the cutoff into Durango). It's not operational yet, as I've got some fine-tuning to do I suspect, and the wiring. But basically the rails over the entire Ophir loop, and both high-line and low-line, are complete.
I ended up using a #7.5 curved turnout for the Ophir spur, and the only one available was code 83. But, I found that using code 100 rail joiners worked very nicely to join the code 75 and code 83 rails. The oversize joiners are just sloppy enough to let the rails float a bit vertically, and it was trival to hold them in vertical position and solder them. I was actually kinda worried about this junction, but it turned out to be really simple and easy.