For budget or stock-style rebuilds, it's hard to beat the value of Sealed Power cast pistons. They are made from high-quality aluminum alloys and feature a carefully controlled casting, heat-treating, and CNC-machining process. And, because they're designed and manufactured to exceed OEM specs, they'll provide improved reliability, performance, and a long service life. (1966-1975) Chevrolet, Chevy Trucks 250 CI L6 Inline 6 cyl. Bore 3.875, Rings 5/64-3/16, Pin Dia .9275. Recessed Head.