Horn question

My 69 340 swinger has 1 horn that looks like it came of a Ford or Chev. The guy I bought it from said he couldn't find the 2 that came on it so he just put something that worked to sell it. I would like to know if the factory ones have a correct number on them for each year or is it anything goes ?
Mopar used at least a couple vendors for horns. Prestolite and Sparton come to mind. The brackets are what make them fit your car. You may be able to modify others to fit. They come up for sale here from time to time. Here's a couple I found on E bay for my 70 Swinger. It originally came with 1 horn.

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