Hi Alvin, welcome to Outdoorking.
Our reel mower guru, Deejay, is interstate at present but will get back to you remarkably soon despite that. Meanwhile, could you post some pictures of your SB45 please, so we can work out just what you have.
The 45 on the model plate means Model 45. The serial number is unfortunately undecipherable because SB used no particular system for allocating them. We normally identify them from the photographs, plus if it has a Briggs and Stratton Engine, and it is the original one, from the long series of numbers stamped on the cooling air cowl. These tell us the engine's date of manufacture. However the early 17 and 20 inch ones, and the slightly later 14 inch ones, had Kirby Lauson engines and those did not have serial numbers which are as easy to decipher. Because you say you have a red engine with a cylindrical air cleaner, it sounds as if it has a Kirby Lauson engine, but the pictures will clear this up with certainty. Please include a picture of the engine identification plate on the crankcase.
With pictures in front of him, Deejay will be able to tell you quite a bit about just where in the series of design changes your mower can be found. He can also tell you whether it has non-original parts. If you supply pictures specifically showing the blades of the cutting reel, and if you remove the chaincase cover and take pictures of the chains and sprockets from a camera position in line with their mounting shafts, he will be able to assess their state of wear.
