I assume your catalog number is 8187RN. The first "8" designate a "Toolroom" lathe. The "187" designates a Heavy Ten. The "R" is for a 4-1/2ft. bed. The "N" I'm not familiar with off hand. That letter is supposed to designate the drive type. Typically it is a "B" but back in 1941, I'm not sure what they might of used for drive designations.
The rest I'm a little confused about. Is the 102 the unit code? All SBL's used a unit code on all major sub-assemblies. I'm not sure about the 13-3/4" spindle. I've never heard of that. Typically, the Heavy-Ten had two available spindles. They were the 1-7/8" x 8 tpi spindle and the larger 2-1/4" x 8 tpi spindle. Spindle size was coded into the serial number using the suffix letters at the end (but I think SBL didn't start using suffix codes in the serial number until 1947).
