Not necessarily, especially if they're not standard bore size (3.5"). I believe all 216s and early 235s had cast iron pistons. If they're aluminum, they're definitely aftermarket. Common oversizes are .020, .030, and .040" overbore, possibly even .060 or ,080. and they can be cast iron or aluminum. Measure the cylinders (not the pistons) for tapered wear, and if the taper is much more than .005" from top to bottom of the cylinder, you'll need to rebore the cylinders and install oversize pistons and rings. At 2000 RPM, rings in a taper-worn cylinder have to flex to maintain contact with the cylinder walls 60 times per second, resulting in very short ring life and really bad compression sealing and excessive oil consumption.
