Yes those with the valve reliefs are 2bl pistons. All of the 273 blocks started life out the same. They didnt differentiate between 2bl and 4bl at that point from the factory.
We would have put EGGE pistons in ours, but cost would have been close to $1k to our doorstep in Canuckistan.
I have since found and bought a used set. I hope to build around someday lol.
TMM has you pointed in right direction.
There was a guy on here that bought a new commando rotating assembly I had never heard of before?? Not sure where that thread is...
