Need help with sb 10l - 8187-YB Bed Serial ****RKL11

I just acquired a Heavy 10 circa 1953-1954 from the estate of the original owner. It has a 3ft bed, came complete with the original taper attachment, tailstock, cushman 3 jaw, 5c Collet Closer and UMD assembly, looked like something worth saving (it was being sold at a reasonable price). Since most of these machines were shipped with their own stand, the machine seemed a bit odd to me as it was mounted by the owner on a homemade bench. I'm not unfamiliar with SB lathes, but I can't find any info on PM or elsewhere regarding an 8187-YB. The Model "A" designation is also slightly confusing, but it looks like everything is stock to the lathe. It didn't hurt that it ran fine albeit slightly noisy from the spindle, maybe bearings or lube? I'm hoping there's someone who has seen this configuration and can fill me in on the meaning of the "YB" after tool room designation 8187. I also would like to know what a "precision" lead screw is as compared to a standard engine Heavy 10L with a "standard" screw, i.e. was it ground differently, etc. I guess it wouldn't hurt to ask if there are any manuals for this particular lathe, but I know the taper is standard, the chuck is threaded, and its fully operational, including backgears. Any help or information available would be greatly appreciated. Pics attached

Y = 3 foot bed. B = Tubular framed bench with drawers.

If you download the 1952 Catalogue from Steve Wells SB Workshop site you will find your lathe in there.

Skilly

'Toolroom' heavy 10. You did not give us the serial number, so we cannot date it, but given that it has the narrow ratio gearbox, I would guess 1951-52 or so. There is nothing special about the leadscrew at this point. 60+ years of wear have undone any improved precision.

allan