The small size of the WW carb may appear to fool some that it's a 1bbl but like AZKEN says look down the throat of the carb. Quite a few years back someone on Jolly's site told me they had a 1bbl on a 64-65 305E, I thought that was odd so I had the person post a pic of the carb on the engine and of course it turned out to be a WW 2bbl which was a surprise to the owner of the truck