Phaestos:
You wrote: "I don't think it's totally homemade, but it's got a strange extension under the gear box that does look homemade. "
Alright, here's a hypothesis:
The lathe is a standard loose-change lathe TO WHICH A GEARBOX HAS BEEN ADDED. The gearbox changed the threading arrangement, so the mechanic, Mr. Moyer, "struck" a new threading chart with number stamps. He "signed" his work, and also added an "owner's mark" to the bed.
This is not as far-fetched as it sounds. Lindsay Books recently reprinted a collection of old magazine articles that described various gearboxes to convert loose-change-gear lathes entirely or at least partially to quick-change. In the days when QCGB's were first coming into widespread use, there were many owners of perfectly good loose-change lathes who wished to improve the efficiency of their shops by adding shop-built QCGB arrangements in one form or another. I beleive there were even a few pre-made QCGB's that could be added to certain existing lathes.
Now, there is of course a certain amount of speculation in this, but it fits the known facts regarding your lathe, especially if Perk is correct that it is really a modified South Bend Junior.
John Ruth