If you are bolting the V8 in and using the six mounts you will need to use the long pump as the motor will sit back real close to the firewall and there will be a big space between the fan and radiator,if you are using the correct V8 mounts you can use the long or the short pump as the motor will sit closer to the radiator. The two pumps are noticably different if you have both to look at and you will need the correct pulleys and brackets for the altenator and power steering pump if so equipped for either waterpump.

1937 Chevy 1/2-ton pickup