I believe what you have is either an OB-C or an OB-70 in the 1957-59 range. I have a 60 that has a rectangular serial plate, 57 & 58s that I had had the oval plates. Not sure about 59. Maybe Del can add some more insight.
Thanks for the pictures. While stripping paint the colors match the ob-70 ad so I'll assume that. It had the lines on the fender from the light panel so 59+. It had a rectangle sticker outline on the winch also.
Well I think you nailed it on the year and model. 1959 OB-70 couple pictures