Most aluminum alloy pistons are cam ground, and that measurement sounds about right. There should be an "invar" strut cast into the pin boss area on both sides to restrict expansion toward the thrust faces of the piston, causing it to get round as it heats up. The unmarked top ring should be OK to install either way. Check the end gap on ALL the 1st. and 2nd. groove rings. A good rule of thumb on end gap measurement is a minimum of .005" of gap for every inch of bore size- - - -around .025" or so for a stovebolt-size cylinder. Since the rings also expand when they heat up, a bit more ring gap is better than not enough.
Jerry

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