This install is using the standard 69T rings. Apparently Santana uses 74T rings that are also 8mm pitch (Gates part number 08745AA10), but I'm not finding any specifications for those as far as ring diameter or spacing requirements. I wonder how much larger they are and if that might be a solution here, if we can't get the belt tight enough... hmmm.

As for flanges on one side or the other I guess that is a non-issue. It would seem the only ring orientation issue as far as reversing them (placing on the inside) would be if the teeth were somehow machined to only work in a single direction of rotation.