The fan in the 68's blow so little air....has anybody been able to find aftermarket fans that can move more cfms' that the stock replacements?

Try a blower from an A/C equipped later model car.

I put one in my 69, (out of a 1992 Grand Am) and the air from the defroster will almost blow the hat off yer head.

The thing to watch out for....

The bigger fans draw more current, so you may want to consider putting a relay in the circuit, and upping the size of the feed wire.

I didn't put a relay in mine, and the orange blower motor feed wire doesn't even get warm, but I don't know what shape your wiring is in.

Try a search, or drop a post in the electrical forum, you may find some info there.

I got a later model replacement and the wiring always got hot and melted the connectors, I never knew they drew more. Of course that same motor squealed from bad bearings so that might've been the problem too. Make sure you hook up that little cooling hose that goes in the side of the motor, lots of people skip that because it breaks off over the years.