Here's the 289 Hi-Po's cast flat-top piston with the C3AE rod. The 289 engine used either flat-top or dished pistons to control compression ratio. Early in production, 260 and 289 pistons had four ring grooves. By 1966, there were three grooves for top compression ring, middle oil wiper ring, and bottom oil control rings. Although it is surely published somewhere that 289 High Performance engines had forged pistons, this was never the case.