[Jeff Lee]

Then I stand corrected. If those engines are unique, then they should get unique HP adjustments.
And after looking at the class guides, the 1969 318 was reduced in all models, not just Dart. So if you have a Coronet, Swinger, Dart, station wagon; whatever, the 318 2bbl is now 172 HP.
But the 1973 was Valiant / Duster / Barracuda & 'Cuda only and not the rest of the larger car line.