This is a hammer (Bridgeport) Ryder made. There's two interchangeable heads, held by an Allen head set screw.
There is an extension handle rod that can be custom bent to make the hammer head line up over the dent as needed. I'm backing the dent up on the outside with a flat dolly and tap lightly on top of the highest point of the dent. Since metal dents of this type still have a memory, this hammer should get it's mind right.