[Mr70]

Exactly how hot a temp. are you reaching at idle?
You should be able notice significant resistance,even once the fan is attached to it.
I've been tackling this very same problem with mine this summer.
Stay away from Hayden brand Ken,as they seem to be not as road worthy on Big Blocks.
GM uses a unique fluid dampner that is more sensitive then most,so aim for that first.I found a real good GM parts wholesaler in Wisconsin that carries defunt fan clutches while others say looong discontinued.
How close or distant is your clutch to your radiator,as you may need a spacer,added or removed,or even your belt slipping under duress.