Saw a pair of avid 7-tooth involute style drivers for the hex shaft on a facebook group for $60. I bought a set of those a couple years ago and they cost me $260 plus shipping from Avid... so that is a deal... I put mine onto my Pro, have not tried them yet. also got a speedo-healer to make the speedometer correct...
The drivers are the ones in the pics I am attaching. No rail trimming required, uses involute drivers and the center extrovert like stock.
EDIT: My bad, he wants $75 for them, in Deer Lodge MT. Tempted to pick up another set for that price in case I sell the Dragon 860 and buy another Pro...