I’ve never heard of 58’s being leftover 57’s but it’s possible if OMC was retooling for the ’59 T Stat models. Rope start models weighed the same for both years but I’m not sure about the five pound difference on the electrics. Part of it could be in the flywheels as they have different part numbers or possibly the starters. I do have a small ’58 12 volt starter I should weigh sometime but no ’57 starter to compare it to. The electric starters do have the same P/N though.
Who knows, maybe they were weighed without any oil in the gearcase and that one less rivet holding the emblem on would make a difference to.
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