I have no answer to your question but you are lucky. Egge's were the only piston available when I rebuilt my 273 10+ years ago. That info wasn't available for me either. I got a cc kit and measured with a piston installed.
I’ve been really lucky I think. Parts are very expensive here in Australia. I purchased a full engine rebuild kit out of the States for the price that I would have paid for pistons and rings here in Australia.
I’ve been reading anywhere from 15-11.5cc’s for the Commando Pistons. I read a guy cc’d a set and they came in at 11.5 but just wanted to be certain.
