Hi Paulie,
Firstly welcome to the ODK Forums.
Your machine is not missing it's ID plate and that is because it was never fitted with one originally.
You'll see that it has the white serial sticker on it which states nothing more than the Model: 45 and a Serial number given.
The variant number is no longer given as by this stage of production there were not a number of different variants available like there was in earlier times. Simply all that was available was the 17 and 20 inch machines, both Briggs powered.
Am I correct that yours is the 20 inch machine as it looks somewhat wider than the 17 in your included photo. I'd also say that yours was built around 1979 to1980 during the Challenge Banks time of Scott Bonnar ownership.
Cheers,
BB.
