I took twin Olds Ciera (V-6) fans off of mine that were a part of the original conversion. They didn't come close to moving enough air to handle the 5.0L with a/c in the southeast summers. I installed a fully shrouded dual 11" SPAL set up that moves about 2900 cfm of air and it works wonderfully.
Cooling is no place to take a chance or a shortcut as the consequences of a bad choice are often pretty big problems. As I said before, I can't imagine why anyone would think fans designed to cool a small 4 cylinder would be sufficient to meet the cooling needs of a V-8, but if you want to give it a try, go for it. It helps that you're up north and have lower average ambient temps to deal with. Do you have a/c? If not, that helps too of course.