1. Circle k stings are a ss/nickle "hybrid" according to their website...
2. The sunbeams i have been using for years are nickle.
3.most every flatwound i prefer is nickle.
All of these strings seem to have a softer feel to them,so i can only imagine that along with being easier on your fingers,they are also less abrasive to frets as well. In fact DR makes that claim for ALL of their rw strings. "Won't eat your frets"....also,in a 40-100,seem to be fairly low tension,which is probably desirable for that '72 of yours.
This is what i was trying to convey,but upon reviewing my initial response,realized i had not really done so.
