That's a sort of a "Frankenlathe". All Atlas but parts from different models and years. As received I believe it was a 1935 vintage, had a ZAMAK compound, 5/8" leadscrew, no power cross-feed, single-piece carriage/apron, separate cast iron gear covers with no belt guard. I removed the gear covers and added the belt guard, pulled the leadscrew and replaced it with a 3/4", put on a newer carriage to gain power cross-feed and replaced the compound with one made from iron.
There is no model number/serial number name plate, no evidence of one ever been attached to the bed. The only SN is on the top of the ways at the tailstock end: L6-860 Bed is 42" long rendering 24" between centers.
PS:
Changes since that photograph was taken: It currently sports Compound Rest Assembly 3980-75 and Cross Slide Screw Assembly 3980-18
(see Owner's Manual and parts list for 101-28900/101-28910)