1965 273 Heads

PolarBear....Yes the compression (and power) comes from the high-comp (higher squeeze) pistons. The 273 "Commando"(Plymouth) and "Charger"(Dodge) engines have 10.5:1 compression and the 2 barrel engines have 8.5:1. The 4 barrel cam is also a hotter grind. That grind is not available today,but you can probably get an aftermarket cam very close in specs. The heads,block and exhaust manifolds are all the same,be it a 2 barrel or 4 barrel motor. A stock 2 barrel motor definitely performs better with a 4 barrel installed,but still not as good as having a true Commando engine. Good luck with your project

Hope this helps...