Roger your old arms off your 41 deck should work on the 50 deck. Just knock the roll pins out of the shaft and move it over to the 50 deck. Your mule drive will work on the 50 also. If you want to make your own mounting plates go ahead but I would just knock out the roll pins and go on. This is my 317 I just put a 50 under in place of a 46.
Later,
Justin

Later,
Justin