Difference in 273

I'm not sure about the valve springs. I haven't seen any documentation on that. And I believe the chrome PCV cap was only up thru 66.

Note that the Commando 273 engine package was completely independent of any performance suspension or brake packages. When you ordered the Commando engine as a line item, that's all you got. The HD suspension (heavier leaves and t-bars, with front sway bar) came with the Formula S option on Barracudas, or could be ordered as a separate item. Now, you HAD to take either the Commando 273 or the Super Commando 383 (67 up) when you ordered the Formula S package, but it didn't work the other way around (for the 273 -- Formula S was mandatory with the 383 in 1967). There were no accessories or dress-up items associated with the motor other than the Commando badge on the fender. My 67 FB was ordered with the Commando 273 as an extra cost option, plus HD suspension as a separate line item, minus sway bar (for credit), plus manual disc brakes (separate line item). It was a bench seat, column shift auto car.