Hi Matt, This is a great idea of yours to establish a registry, however, sadly, it will be almost impossible to establish an
exact date of manufacture because of so many variables. The later Briggs can be dated due to the manufacture date being included in the model type code.
Unfortunately, Scott Bonnar/Rover-Scott Bonnar did not include such a date code on the chassis itself. Even the mower numbering sequence may or may not be a source of dating information (eg. did they start every new model change with Number 0001?)
With my Model 45 even my info is a bit sketchy, owing to the fact I scrapped the original engine without recording the numbers, and my original handbook (and receipt) were lost in my last move with the RAAF; but I have to following info for you on the chassis:
Model No: 450520 17" petrol
Mower No: 07773
Original engine type: Briggs and Stratton 2.5 HP Orange in colour.
It has a 2 rail engine deck
Vertical chain case screws
Scott Bonnar round decal on handle cover plate
Scott Bonnar shield design logo on catcher and chain case cover.
Original Scott Bonnar embossed handle bar grips
Original rubber grip on clutch lever on handle bar.
Paint is original (sort of olive green hammertone).
Plastic front roller end cap inserts.
Plastic grass deflector adjusting knobs.
Anodised aluminium data plate in red.
Hoping this helps with your data collection, Matt.
Best wishes with your project.