The lower pulley is from a Ford of some kind, PN: E25E6312A7A.
Outside diameter is 7.5 inches. Only mod was opening up the center
register (slightly) for the Pontiac size and picking up the larger
Pontiac bolt hole locations. The bolt pattern is just wide enough
that you need cap screws for clearance. Total tome invested in the
lower pulley mod was less than an hour.






The alternator is from a 90 GM truck, and it fits low on the right
side with about 3/4 inch clearance from the head. I still have to
finish up the mount for the thing but it looks like it will be slick.

I also wanted to try drive the water pump, so I added another Ford pulley.
This one is PN: 1626162MR and because it it a crank pulley, it required me
to machine a hub(pictured in the first post)to adapt it to the Pontiac water pump.
Not exactly an elegant solution, but it is just an experiment. When I go to the
electric water pump drive, I just change to a shorter belt.

This is six rib- Matches the common GM stuff. The lower pulley is off the 5.0
engine family, I think. Total depth is just under 3.25 from the face of
the balancer forward.

This shows the water pump pulley and the hub I had to make. I think the water
pump drive looks like hell, but it is only an experiment until I run the electric unit.