Is the owner/builder's name Jiang or something similar? (A Chinese name in 1950s Japan?)
I've managed to find the page on this vehicle, but approximately 75% of the Japanese text has been rendered illegible. Below are the humorous results of three separate attempts to translate the text. Earlier attempts produced the terms "Rhine" and "Rheingau" (you mentioned the name sounding German), but this is missing from the later, presumably more thorough translations.
I'm still working on it!