I think the Optimus 350/350cp is an earlier example. It has the bakelite? knob, riveted tag, no Arabic, no stamp dates I can find.
You are right about the 350 being the early version. There are no date markings on these lamps, so the only way to tell is by the fittings. This model was introduced in 1957 so a guess would be it is from 1957 to 1960.
@Nils Stephenson If the 350 is from 1957, where does the 300P fit in? Nice lamp @Rob Mikell. A bit of polish will have it gleaming.