I think that carb is one of the ones for the navy version of the lightfour models 4375, 4376, and 4377 of the 1943 vintage. Those motors came with a "rebuild kit" which was a box full of spare parts which included this 275787 carb. That is also why most of them you find are stamped with the US bureau of ships stamp as well. This also explains why there are so many NOS ones around. If you look closely at the photos in the link below you can see one of the boxes in the rebuild kit has the 275787 cab stamped on it. Hope this helps. http://www.ahlstrandmarine.com/products … -1943.html
The Big four primer cup is 201144, the Lightfour primer cup is 201764, the Sportwin primer cup is 202119 – I don’t have a parts list on the Johnson QD12 which has a primer. . . 🙄