MRL 340 for the 21st Century

MRL Performance said
Racetech pistons. Piston weight is pistons, pins, locks and rings together. Bobweight was around 1900g or so
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so this is not an off-shelf piston or is it? I just looked at the online catalog, 18* chevy and flat top chrysler. my math doesnt add up when you use a 6.250 rod...