Hi Steve, and welcome to Outdoorking.
You raised a lot of points in your post, and most of them are best answered by Deejay, our resident SB guru. However with regard to dating your mower, as Padman said, the numbers on the air cowl of the original B&S engine are the best estimate we can make. If you post the whole long string of numbers from the cowl we can tell you a few things about it, most of which you won't care about since you've pitched that engine anyway. The last block of numbers includes the manufacturing date.
From past explanations supplied by Deejay, I understand that matching the reel to the bedknife can be done either by lapping them together on a jig built into the special-purpose grinding machine, or on the mower itself. The reel should be spun backwards to do this because otherwise the grinding paste will round the leading edge of each blade, and the bedknife as well. The process is a bit fraught with difficulty either way, because typically the reel bearings have a little bit of slack in them, especially if they are not new, so lapping on the mower is less than ideal. Nevertheless backlapping on the mower, so long as the bearings are new and the parts are already sharp, seems to be able to extend sharpening intervals and perhaps slightly improve mowing quality.
The colours on that late SB-type mower indicate it is a Rover, not an SB. Rover bought SB and continued manufacture of the model 45 with very minor changes. Deejay can tell you what they were.
