I was able to fit a GM 10si alternator on my stovebolt 216 perfectly by flipping the original bottom generator bracket end-for-end, and flipping the top bracket upside down and bending it slightly, and the pulleys line up perfectly. You can elongate the hole a bit to adjust it if it doesn't quite line up. I swapped the pulley on the alternator with the one on the generator, keeping the fans on their respective units. It's really pretty easy, but if you want to make your own bracket it's good auto shop practice. You just need a flat piece of strap iron with holes drilled in the right places.

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A lone amateur built the Ark. A large group of professionals built the Titanic.