Hi Shifty, the age of your engine by grumpy has identified it as being manufactured in 1970 and that fits with the chassis, which is an early model 45....
The Model 45 was first introduced in 1968, and yours can be easily identified as an early model by the alloy end-caps of the front roller and horizontal screws on the chain case cover and the screws for adjusting the grass deflector....( it can be considered as a Mark 1, so to speak ) It is a 14" cutting width and was designed for use on smaller lawns...( the 17" and the 20" for the larger lawns )
Once sharpened and correctly adjusted and maintained, it should give you hours of mowing pleasure.
