The sleeve was almost perfect underneath all that stuff, with just one or two very small stains and certainly no rust. BSA must have been looking way into the future!
I’m curious to know when and why the chain line in the primary chain case got changed. I guess that, in the day, you would have gone into a BSA service department, quoted your engine number and be given the correct part (in theory!) but here we are sixty some odd years down the road and many of our bikes have been ‘mixed and matched’ (and in the case of my bike, not very well!), so unless you can be absolutely certain that your bike is 100% original, frame and engine numbers can be useless when it comes to to such things!