...FYI, from all the original factory photos I've seen, the 273 Commando came stock with a fixed FOUR blade fan, just like what's in my car. At least from what I can tell, that's what's original for a non a/c 273 4bbl...
I've had 3 untouched Commando 273's in Formula S cars. Two 4 speed trans, No AC. and 1 automatic trans from 66 and 67. They were 7 blade fixed fans. I could see yours coming with a 4 blade fixed fan. Nothing is for sure with Ma Mopar. I had the same problem, overheating in stop and go traffic, with a 70's Dodge PU truck. A Factory flex fan fixed it for good, no other changes. Good luck, seems you are on the right track.