ok,yes you may use the lower Y slide bracket with the non a/c alt 3 hole bracket it would share the same lower side bolt on the water pump
on non a/c alt bracket the pivot bolt goes into the hole in the head,bracket for front of alt on pivot bolt with spaces in place,2 long side wp bolts holding bracket
now the alt is hung..
swing arm goes on lowr side wp bolt to swing up to alt bolt
the bracket you need goes across the bolts on the top of wp
this is a/c brackets,the alt pivot bolt does not goe in the head but into the offset hole of bracket with pivot bolt and nut...like you have now
all you need is a a/c comp front bracket to support the front of the alt and push it back in line
you have a belt straight to the crank bypassing the a/c comp now
it may need to be a little longer when you get the front bracket
dont look at the BB pic posted
and when looking at the SB pics they have non a/c brackets and pullys so you cant get that with what you have on there now
you could take some flat bar and drill holes in each end then support the front of alt from a water pump bolt,line it up with the belt off and get it supported first then install a correct length belt
if you look at the sb with a/c,you see the 2 belts over the top of the a/c comp going to the alt,you need that front bracket on the a/c comp
then run the belts down to the crank like you have it now
clean up the web/rib on the wp neck and you will get both belts like the a/c used on the alt
if you want a true later style non a/c set up you need a non a/c 1 groove wp pully and a 2 groove crank pully for ps
they have a single groove crank pully for non a/c manual steer also when your looking so remeber 2 groove for ps
also looking at the sb pics some of the non a/c brackets have 3 bolts in the wp and the alt pivot bolt into the head...those are for an early style cast iorn wp.. may or may not work on alum wp
but the exploded pic of the brackets are what you want with 2 correct pullys to match for non a/c and ps
now you fused?