Hi to Mosic, and a warm welcome to the forum. It's good to have another potential Scott Bonnar owner on board.

If I was looking to buy this 20" Scotty, I would first like to see inside the chain case...there could be worn sprockets (pointy teeth) in which case both the sprockets and chains would need replacing. They are expensive items.

You may like to consider this; the reel has plenty of meat and looks like it may never have been sharpened, that's a good thing...but check the number of blades on the reel, the later 20" models had eight (8).
This machine is an early 20" ( we can tell that by the front roller end-caps and the grass deflector screws) and looks like its had a hard life.
The cutter clutch need re-installing, and as you say, the cork lining replaced. It then has to be adjusted.
I would bet that the bottom blade needs replacing and the new one sharpened at the same time as the reel is done; $70-$100 for both.
The reel bearings (2) should be also replaced at this time. The cylinder reel adjusters could be worn and need replacing, as without serviceable adjusters, the reel will suffer very quickly.
A missing catcher...as you say up to $150....
My vote...give it a miss...especially at $300, another one will come up that could be a later model in much better condition and with a catcher and a Briggs and Stratton engine...The Kirby-Tecumseh's are hard to get parts for these days, and on a cylinder mower, you need it to be reliable.
Once again, Mosic,
