I forgot to mention that if the bed still has the nameplate, the model number and/or serial number (serial number may be stamped on the top of the right end of the front way) can be a clue. Model numbers on a 10F will be of the form:
Vnn
Hnn
TVnn
THnn
where "nn" is the nominal bed length (36, 42, 48 or 54), "V" means babbit bearings and originally shipped with a vertical countershaft, "H" means babbit and horizontal countershaft, and "T" means Timken (tapered roller) bearings. Most serial numbers are straight numeric. Some have an "S" suffix, which no one seems to know the meaning of. A few have a "D" or "DT" prefix which I take to have been made during the 10D to 10F transition period.
Model numbers on a 10D will be 10nn (where "nn" is the bed length). Serial numbers probably have a "D" or "DT" prefix. Although if yours has the latter, the bed and headstock didn't ship on the same machine. There may be an "S" suffix. If your model number has an "A", "B", "C" or "E" suffix, it was originally a Unit Plan machine and certain subassemblies were bought and added later.
Robert D.