I just purchased a set of pro taper YZ foot pegs and they do fit my 2011 300, however:
1) The right side pegs needs serious grinding to allow even partial folding due to interference with the rear brake lever. Gas Gas pegs are cut asymmetrically to allow folding clearance.
2) The pivot of the YZ foot peg is mounted further aft than Gas Gas pegs. This moves the base of the foot peg further forward and reduces the amount of room between the tip of the gear shift lever and the foot peg. I could barely get my foot under the shift lever with the YZ pegs installed, so I re-installed the stock pegs for now.
If someone offers an extended shift lever I might consider re-installing the YZ pegs.
Steve