My '67 came w 26" and air, 383. No 496" w air. I've tried 3 different electric fan setups w shrouds. 2 spal fans, 2 Ford contour fans, 2 CCI fans. All in shrouds w covered slots for more airflow. At idle, all did well, but on interstate, all restricted airflow with temps climbing over 220. I have serpentine setup so am limited to type of mechanical fan. Also only 3" of room between w/p pulley n radiator core. Ended up w a 19" 11 blade nylon fan from Chevy 496 truck. Direct drive, no fan clutch due to restrictions. With factory shroud. I'm in AZ w 120+ temps. Idles for over 2 hrs, oops, at 184° and interstate at 176°. Largest, most blades mechanical fan and shroud!!!! Also make sure your w/p pulley is 20-30% smaller than crank pulley w/ a/c. I also run 50/50 coolant and add 2 bottles of water wetter.