My 64 225 came with a 9-1/4" clutch but when I rebuilt the drivetrain I went with a HD 10" clutch (think Taxi) that I bought from Rockauto for about about a hundred bucks. It does require special small head pressure plate attaching bolts that I got from Brewers. Sticker shock....$36 for 6.
But 2500 miles later everything is good.