Electric fan

Considering the I6 came with a mechanical fan...there are no "right" electric fans. To answer your question though, people seem to have good luck with the Taurus fan...not sure whether it fits the smaller 66 radiator...but installing a larger 67 radiator is a matter of minor trimming of the radiator support...if originality is a concern you might not want to do that though(which it usually isn't with a plain jane T code coupe)

wicked is right, go for the taurus fan and larger radiator. the taurus fan should be quieter than aftermarket fans, and pulls enough air through the rad to keep the engine cool. i recommend running a relay in the system, preferably one controlled by a temp sending unit, and upgrading the alternator to the 130amp 3g unit from said taurus. this way you will have plenty of power to run the fan and charge the battery.

here are links to various electric fan installs, some early cars some fox bodies, but they will give you lots of information;