I am very thankful for your help. Getting the pulley sorted out is an important part of finishing the refit
on our boat. I'm a US citizen living in Oman and our boat is in the Philippines
so it ain't easy getting things sorted. We're headed for an end of December departure to go cruising but we keep blowing out the seals
on the pump. Here's McM Carr's note on 1/2" bore pulleys.
Cast Iron—For Type A (4L, A, and AX) and Type B (5L, B, and BX) V-belts. Pulleys have standard ANSI keyways (except for 1/2" bore sizes, which have no keyways). See About Couplings and Keyways for ANSI keyway dimensions.
Maybe we can rely on the set screw but I sure would like to find a pulley with a keyway. I've already ordered to sets of new seals