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That's definitely a tough one. I don't think that the stamp left of the four is a letter. It looks more like a 3. So I would look more at the stamp to the far left. It looks to be an L, so L C would be February 1956. The 550-1 was manufactured ~ 1949–1970s. Sorry, I know it's a guess, I wish I ...

Hey all

First time posting, I recently found grandpas long lost 550-1! Thing is in rough shape but now we have a project. I am having trouble deciphering the letter code for the year on this thing and was wondering what others think it could be.

Thanks in advance https://imgur.com/gallery/date ...