The only problem interchanging 71/72 and 73/74 hoods between them is when trying to fit a 71/72 into a 73/74 car. A vertical "filler" on front of hoods of 71/72 hoods is larger which disturbs with 73/74 top of fender brackets with bumper because these brackets are wider and straight on 73/74 while 71/72 are like wire shaped and angled to sway this filler. So this filler must be trimmed out to fit the 71/72 hoods on 73/74

The other way around ( 73/74 into a 71/72 ) is not a problem.