Namely between 72 (good year so I gather) and 78 (well into the emissions era and the truck I just bought). I was just looking on rockauto.com and it lists the same part numbers for cylinder heads in 72 and 78 so that's not helpful, how did the heads differ? Camshaft? Intake? I already know about the retarded timing gear Ford started using after 72.

 

actually 72 was a bad year unless you have the police interceptor d2oe heads... the d2ve heads suck unless you want to run race gas- theyre very detonation prone. from 1973-1978 it doesnt matter- theyre all the same engine, just changes in the ignition system. in 1979 they went to an external balance engine but left the top end the same as the 73-78 until they went to fuel injection in 1987-88

 

If I am not mistaken 72 was the first year for the retard on the timing. If you change to a straight up TDC timing chain it will really wake the engine up.