Ray,
We're handicapped by not having anywhere nearly enough hard date versus serial number data plus no information on when if ever Atlas started over with serial numbers. And Clausing has no manufacturing history data. However, what is the model number of your lathe? I think I figured out from reading between the lines that yours has a QCGB, which the UK site says first appeared on the 10" in 1948. However, if your nameplate doesn't say QC something (you didn't give the bed length) then the presence of the QCGB doesn't tell us anything about the age of the lathe. The presence of Timken bearings doesn't tell us anything, either. I have what I am pretty sure is a 1935 Atlas catalog which says that any Atlas 10" can be purchased with Timken bearings.
The only sure way to pin down the date to about the closest year is to pull the spindle and check the dates on the two bearings. Whichever one is later will set the earliest possible date. Depending upon questions we don't know the answers to, the actual date of manufacture could be up to at least one year later (widest spread anyone has reported between their two bearing dates).
Robert D.