what you have isn't japanese made, imo.
i also tried to find history of singer taking over, but i couldn't. where did you find that info?
i ran that picture because it has the same shape and the hand-wheel is the same. in the picture it also showed a serial number (i think) so i thought it might be a starting place for research.
i think you're right about the year - early 50'5, maybe late 40's - but that's a guess only. there are a couple on ebay right now, but no dates and no cabinets like yours. there isn't much info out there, is there? it's very handsome.