Hi cory.m,
Firstly welcome to the ODK forum.
There's lots to learn here and heaps of info that will keep you going for months, maybe years ?

Now as far as your Scotty is concerned and the limited amount of photos you've supplied, it's a series 1 machine fitted with a Kirby engine. That's about all I can tell you as the ID tag doesn't tell us much at all.
If the engine is the original it will either be a 17 inch or 20 inch machine as on the engine plate you've cut of the number that's stamped into the plate above the Spec No.. It will more than likely show HK25 or HK30. If it's HK25 then it will be a 17 inch machine that was made between 1968 and very late 1972. Only Briggs powered units can be more accurately dated but the use of B&S engines didn't start until 1976 across the full range. The 14 inch model was powered by the B&S engine from the start of model 45 production in 1969 using the small 2 HP Silver painted engine until Kirby engines were used across the whole range for a short period of 4 years between late 1972 until the end of 1975.
Are you confused ? I'm sure you are, but that's how confusing it was for us to work out the timeline for the life period of the Model 45.
Cheers,
BB.
PS. If you could post up some more photos of around the mower I might be able to give you a better insight.