OK. The engine is ‘55 block which has a low mounted water pump.
Therefore, I should measure the damper/crank pulley to see if it’s 6 5/8” and if so, go with a 7” water pump pulley. And also measure the width to figure out if the damper pulley (or engine) is from a car vs. truck so that I get a water pump pulley of the correct width.

Thanks,
-Mike

1955 Chevy 2nd Series 3100 Stepside, 235cid