The Scott Bonnar history question (when was it made) is a perfect one for Deejay, but he's away celebrating his father's birthday and so may not be able to help right away. The short summary, though, is it appears from the serial number to be a Scott Bonnar BonMow, introduced in 1953 and I think produced only in the 1950s. You can read a little about it here:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=14559#Post14559

That is a rare collector's mower, and seems to be in eminently restorable condition. You may find you get one or two Private Messages on Outdoorking from collectors or restorers who are interested. I could not estimate its value, but it will be increasing with time, and it deserves to find a good home.