A-Body 440 cooling problem
First things first. Find out why the belt is slipping, is the pump hard to turn? The single belt drive for the pump-fan is more than adequate however I've never used an 8 bladed fan only a 7 or 6, but this might have been installed at the factory because of the Air Cond. Also if you haven't got a slotted belt like the Gates gatorback then get one, they're more flexible around tight corners (like the alternator sheave) and tend to grip better and slip less. If the belt still slips trying to drive that big fan then use 2 belts for the 2 grooves but they have to be "exactly" the same length and as said before you need a shroud.
Terry