Heads, Intake & Carb upgrade...

Something else occurred to me:
If you're intent on using those X heads on a low comp. shortblock, with your compression not up to snuff you could consider boosting the engine and forcing more air in there; but that takes up valuable under hood space on an A body, and another cam revision... Chinese Ebay supercharger/turbocharger kits aren't outrageously expensive, but blower motors are way out of my wheelhouse so you'll have to do your own research there.