granted - that flywheel bore looks shot .... and as mentioned, the "key"
or nub or whatever you wanna call it is cast into flywheel.
FWIW, I have a 445, and a few years back, that nub wore off - the flywheel
wouldn't hold on the shaft. I took a small jewelers file, and filed a groove
in the flywheel arbor to match the grove in the mount shaft, and then clipped
a finish nail with a diameter that matched the slot size, slipped it in as a key,
and that saw's been run'n fine since. YMMV