360LA Clutch Fan

^^Agree.
A bigger concern would be which water pump/tc cover you're using- '66s were designed to use the (pre '70) cast iron water pump (driver's side inlet) which is considerably shorter than the '70 and later aluminum water pump (pass. side inlet). I'm not sure you'll be able to find a short enough fan clutch to fit the long-nose aluminum pump in an early A body ('66 and earlier-smaller engine bay than '67 and later), especially if you've got a thicker than normal aftermarket radiator.
The Hayden #2947 fan clutch is about the shortest one I know of (although I've read rumors of an even shallower MB clutch, but can't verify) if you intend to go with the late water pump; and even that may not be enough. The early iron pump should give you sufficient clearance, though.