Reverse rotation waterpump, not cooling.
Often the late 80's early 90's 4.3L Astro vans have the old style V-belt routing but the serpentine belt. That is what I used on my 97 Vortec with a new 78 350 waterpump.
If you want the V-belt routing and V-belt pulleys anything from 70-'87 or so should work.
The only problem you may have is the 3 point top alternator bracket may interfere with the intake as some originally mount to the intake.