Hi Salty, welcome to Outdoorking. If you give us the long string of numbers stamped on the cooling air cowl of that Briggs and Stratton engine, we can tell you what model it is and when it was made. As Jarrad said, it does not appear to be the original engine for that mower, but many - in fact I think most - Scott Bonnar 45 mowers had Briggs and Stratton engines, and we should be able to tell you if you have a correct type that was used as original equipment. Our SB guru, Deejay, may be able to estimate very approximately when your mower was made, and we can tell you when your engine was made too.
As far as I can tell from the pictures your mower seems to be in sound general condition. Please tell us whether the two clutches work, and whether the engine runs properly. If there are faults, we can talk about how to overcome them.
