340's, no. Lots of them got scoops installed at the dealership level.
NHRA probably allows them on any 71-72 car because the twisters got the scoops. Are they correct, nope. I'd like to find a 71-72 340 Duster with an original fender tag or broadcast sheet that has J54 on it. Never seen one. Seen plenty of repro's that have the number, no originals.