Technically, Zamak is not pot metal because pot metal is any of a bazillion slightly different lead alloys. Ideally, Zamak contains no lead. And in fact, contamination of the Zink with lead is generally thought to be the cause of Zink pest, which causes the failure of Zamak parts. Also, it appears that the specific Zamak alloy used by Atlas was Zamak V.
If the Serial Number is stamped on the name plate, it does not appear to be found anywhere else on the machine. Given the propensity for new owners to remove nameplates when disassembling a machine for painting and to never bother to reinstall them, we have an unfortunately high percentage of machines that, with the exception of 10" and 12" lathes with Timken spindle bearings built prior to about 1952 cannot be roughly dated. The database has one entry for serial number 001202 saying the the S/N is stamped on the front of the right knee way. Serial Number 003493 and several higher numbers have a note saying that the S/N is NOT stamped on the way. Anyone on here with a shaper S/N between 001202 and 003493 please report whether your machine does or doesn't have the S/N also stamped on the knee way.
The presence of the "A" in the model number on your nameplate means that when originally shipped, it did not have any belt guards. Good job on someone's part in finding and installing the appropriate guards. Best guess for a date is 1941.