Which engine?

There is no way to tell a Commando 273. I'd drop the 273 into the Commando car. Install a E-4 Isky cam in it with matching valve springs. Add a double roller timing chain. Next would be a 64-65 4 barrel intake and carb. Close enough. Commandos were 65 also. The intake bolts are smaller and at different angle as 66 up heads. 65 are heads are nice closed chambered heads that flow better than most later heads. Add a 4 speed and you are good to go.