Stop in for a cup of coffee

Mopar Tim said
Fan on the car is a 6 blade 17 inch. 20 inch opening seems excessive

Factory fans in '68 is 18" IIRC. 1" clearance is prob as close as one would want considering tolerances and how much an engine moves around. Also the factory fan is notched to clear the bubble top better. At least thats why I think its notched.

here's the fan that goes with a clutch set up. I thinlk the fixed fan is the same diameter, and big blocks maybe got an 18.5" fan.