I have an overheat problem too, one issue is it's a Pontiac from the 60's, they've been known for cooling issues, god knows I'm having mine too. I would never change to an electric fan, just to gain 2-5 HP, I would of changed the radiator to an aluminium rad. and use a clutch fan, that's my next option.
The car isn't designed for electric fan's, if it ever fail's Goodbye engine, especially a hot running Pontiac, I'd trust the belt's because there is more than one there, both don't always break.
As far as Water Wetter, heard about it, and some say don't use it, it does nothing at all, I've talked to some on Highperformancepontiac and they swear it does nothing and use proper 50/50 antifreeze.
I was also under the impression Water Wetter worked it's best with only distilled water, with antifreeze it worked so-so.