I was looking at your pictures and it appears you are using the brackets like shown in the middle row of my post
Middle Left - 354527
Middle Right - 355789
My pump that has the pressed on pulley like your also has those same brackets. On my setup with the bolt on pulley it uses the ones from the top row. That may be the difference in those brackets.
Are you sure you have the pulley pressed on all the way? Those pictures you saved from 1968C30 (
https://67-72chevytrucks.com/vboard/...d.php?t=825218) look like the pulley is pressed on more.