Could be an ICON piston. The step looks weird but just could be the picture. If the top of the step is close to zero deck at TDC then there shouldn't be an issue running those pistons with a modern head. If the top of the step is above the deck height then it is designed for an older open chamber head. I can't really tell from the picture what you have. ICON used to make step pistons for open chamber heads but they weren't a very popular design.