Bob, I have a 505 kit. It has a 6.8 rod and a 4.25 stroke crank. This is the Chevy size of 2.2 bearing size. I don’t pretend to know everything and I like to learn stuff as well as the next guy. Here is a 505 piston in the top pic. Uses a 6.8 rod. Here is the 543 piston in the bottom pic. Uses a 7.1 rod. My kits are the same brand name. Kim
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