From your pictures it looks like your ALT pulley is aft and needs to be moved forward.
It could be as simple as a washer in the wrong place (see attached pic)
You would be surprised as to how many v belt pulleys are out of alignment, normally it’s a small amount even from the factory. Throw in replacing water pumps and alternators it can be visibly noticeable (not all parts are made exactly the same). If you want to fine tune your v belt pulley alignment the technique/concept to figuring out how much shimming or movements of parts are required, I show how in this “How To”
http://67-72chevytrucks.com/vboard/s...d.php?t=318240 concept will work on 6 cylinders.