I have been an SDC member since 1985, and mostly a lurker here, off and on for several years. A person can learn a lot by listening, and that goes for reading too I suppose. However, I have not found much about clutch fans here, so I thought I'd bring it up.
Several years ago I installed a 7 blade, GM, 19.5" thermal clutch fan on a 56 Golden Hawk (Packard engine) and really liked the results: quieter, more air when needed, less when not needed, less parasitic HP loss etc. It mainly involved replacing the Packard water pump flange with a GM flange; press off/press on, since both have the same inner diameter. I then used an GM pulley from a "short waterpump" in GM language, and the rest was pretty much a piece of cake.
I like the GM set up so well on the 56J, that I've toyed with the idea of repeating it on our GT Hawk. I am aware its probably easy to install an Avanti style bimetal clutch fan, but I'd prefer thermal and more blades. I have already determined the Stude flange ID is same as Packard and GM, so it is probably do-able, but has anyone else done this already? If so, I'd be interested in details, part numbers, etc.. Otherwise, I will press on, and report back later.