Not head related but the steel crank 340 that came with my car (supposedly ran) has one cylinder .030” over with a different type of piston than the other 7 standard bore ones!
I remember an article in Hot Rod or Car Craft magazine years ago on this. If I remember correctly, they painted a SBC black and checked under hood temperatures and it seemed to be cooler.
Sure there were 2.02 J heads. Was someone on here questioning that? My 340 has 2.02 J heads-not sure if they were originally or were upgraded at some point.
I always figured it was a box or mold type number, similar to the cavity number commonly seen on molded plastic parts. But, I’m not real familiar with casting processes either, so I could be way off base!!