There's quite a bit of room behind A-body headlamp buckets without getting tangled up into the radiator or hood latch, isn't there? Inner fenders can always be chopped back a bit.
Or were you thinking of clearance with the Duster grill? I can see an external cooler or AC system interfering, but a later latch should be easily graftable into the front of the Barracuda (though, now that I think of it, the release lever for the Valiant/Duster sticks right through the hole in the lower filler panel.
