Hi stu45, and a big warm welcome to the forum. I'ts always great to have another Scott Bonnar Model 45 owner on board, as we all love to learn new things and tinker here.
As far as I can tell, yours is a quite early machine, this I can tell by the early style handle bar logo, but not the earliest, by the fact that it has the plastic inserts at both ends of the front roller.I would hazard a guess at about 1972.
Scott Bonnars are hard to date exactly as the mower numbers did not run in sequence.
Re: the nuts and bolts...I think you will find that all are SAE or A/F if you prefer, and are readily available at any REPCO shop or good hardware place or tool supply company.
Re: the paint.....Ahh...this is where we hit a snag...the formulae for the original green hammertone has long been lost to time...Galmet produce a grren hammertone, but it is too light in colour...The best I can suggest is if you want to restore to it's original colour, you take a piece of the machine to a reputable automotive paint supplier and get the guy to colour match some hammertone finish for you. Hammertone is very durable, hence it's use in a lot of industrial applications.
To remove the engine from the chassis, the clutch, as grumpy has said, has to be removed from it. The nut you can see on the inner clutch half needs to be loosened and carefully tapped down to release it, as it is a captive cotter pin. Once it's down, the engine (once it's bolts have been removed) should slide out from the clutch assy.
Hoping this helps, please keep us updated as you go along.
