If he has the original radiator and wants to run the original style metal shroud, the only fan that will fit the opening in the shroud is the stock 17" unit. That summit fan measures 18 3/4", corresponding with the later stock 19" shroud opening!
Unfortunately, no later style shroud will fit an early A body radiator as they use metal clips on the side of the radiator whereas the later style shrouds bolt to the radiator! Geof