I appreciate the input. I'm rebuilding the front forks of my R90. It was while I was comparing the two styles of fork lowers that I saw this was possible. It comes up all the time but I never do see this solution suggested. I have the much needed right side fork lower piece but I can't use dual brakes till I fix the hydraulics. So I guess I'll have an empty fork lower on the right side till I do that.
I know that machine practices and operations are not what amateurs like myself think they are. Boring or reaming the hole would be relatively easy I think. But creating the flat pad for the caliper seems a bit harder. Still I'm glad it can be done and some day when the price of usable right lowers is exhausted we may see it happening more often.