That was most helpful Willie! The guy's table was not helpful, as it is for the Outdoor scales: 1:20.32, 1:22.5, 1:24, 1:29 and 1:32. (It's interesting that they can get so many scales from a Track Gauge of 1.722 inches which is; or, was the original G scale). So, I needed to use his simplified method of determining Ophir Loops radius, which per what he stated, had a degree of curvature of 24. He stated that I should divide 5729.65 feet, which is the degree of curvature for 1 degree, by the 24 degree curvature of Ophir Loop, So, 5729.65 feet divided by 24 equals 2.74 feet; or, 33 inches. I have to assume that his 24 degrees of curvature for the Loop is correct as I have no way of knowing otherwise.
I have used Google Earth to get a Ball Park radius for the Durango and Silverton's radius at the turn around wye at Silverton, of around 300 feet and the tightest radius at the "Highline", to be somewhere around 280 feet; or, so.
Thanks Willie for that website!