"Thin" rings in metric sizes smaller than the traditional rings were used by GM as far back (maybe further) as '90 in the SBC. Cast pistons are generally lighter than forged pistons. The weight of a piston isn't the determining factor for what the clearance is. Aftermarket pistons are using 1/16-1/16-3/16 ring packages more often than ever. Low tension rings aren't something I would recommend for a street engine.
A 12% silicone aluminum alloy is eutectic, NOT hypereutectic. May be more, but at this point who cares.