Depends on year etc...
Start here and look around (http://chevy.oldcarmanualproject.com/1929_57chevyparts/57cmpc0319.htm).
Look for rebuild kits for today's ethanol gas before you buy a used pump.

You can search this forum for more info. For example (https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/735301/2.html).

If you must have original for a show truck then research is needed to your year.
Most everyday use trucks avoid glass bowls for safety.
Most NOS pumps need rebuilding and have the wrong internal parts for today's ethanol gas.
Buy rebuilt ones from typical classic auto parts websites.
If you need vacuum for wipers, look for dual action pumps.

Last edited by buoymaker; 04/11/2021 2:32 AM.
"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."