Some time ago, we had a client reach out to ask us how to identify a short or long water pump on their Chevy engine. Except for trucks and Corvettes, all models from 1955 through 1968 had short water pumps. They always had the compressor mounted on the passenger side of the engine while the alternator stood on the driver's side. Short water pumps measure from the front to the back where it mounts on the engine block to the pulley flange. They measure 5 5/8 inches for SB engines and 5 3/4 inches for BB engines.
With the exception of the models mentioned above, long water pumps started in 1969 and ran on engines with standard v-belt drives into the 1980s when belt-drive systems became more complex. These longer engines always had the compressor mounted on the driver's side of the engine whereas the alternator sat on the passenger side. Long water pumps measure from where they attach to the engine block to the pulley flange. They measure 7 inches for SB engines and 7 1/4 inches for BB engines.
To determine if the pulleys remain on the car, check between the back of the pulley and the water pump. Except for incredibly small fingers, you should not be able to get in between the setup for short water pumps. Likewise, with the exception of incredibly thick fingers, they should fit in between a long water pump setup.
Here are two additional helpful diagrams from our friends at Summit Racing Equipment to further help identify short and long water pumps:
