273 Commando or not?
It sounds like your car is a correct Formula S car with its original motor, but the only way to know for sure if it's a Commando is to check for the dome top pistons. The only things that separate a commando motor from a regular motor (other than bolt on things like intake, valve covers, distributor etc) is the dome top pistons and high lift cam. Everything else could have been added easily to a regular 273/318/340 to simulate a 273 commando. Pull the heads and look at the piston, the dome top one looks like this:
It sounds like your car is a correct Formula S car with its original motor, but the only way to know for sure if it's a Commando is to check for the dome top pistons. The only things that separate a commando motor from a regular motor (other than bolt on things like intake, valve covers, distributor etc) is the dome top pistons and high lift cam. Everything else could have been added easily to a regular 273/318/340 to simulate a 273 commando. Pull the heads and look at the piston, the dome top one looks like this: