I can't tell from the picture how much space you have Bob, but usually removing the deck doesn't seem to be a big job. Whether what is left of the shaft will be enough to still be strong enough after you cut a keyway, is hard to tell. A keyway would have been a much better way to design it, but it costs more to make. If they used a roll pin for a job like that though, they may have under-designed the rest of the machine as well. Are you sure it's worth fixing?
