Alternator line up
if you have 69 and earlier junk then none of the 70+ stuff works and everything is all fakakta when you go mixing and matching.
do you have the correct water pump on there? that could be a contributing factor; also not all pumps are the same-- some have "taller" shafts so they'll put the pulley further out.
measure the new pulley against the old one and see if that helps put everything into perspective.
i have a 69 and want to keep everything 69, so i feel your pain amigo. upgrading is a PITA and expensive.