Thanks for the thread on forged versus cast pistons, that was great info.
I don't have much experience with pistons, however while doing my topend last time, I switched from PROX to Namura. I found the two pistons to be almost 100% equivalent casting wise, with the exception that the letters "PROX - XXXX" wasn't part of the Namura casting - but everything else matched up completely, even the crosshatch pattern found on the inside of the piston head - and little defects in the surfacefinish on the backside of the skirt.
The Namura piston had anodized dome and molybdenum coated skirt as extra features compared to the prox one - I don't know if this makes a huge difference once running.
Perhaps they somehow use that same source for casting ???