It may be a 3.7 , the carb block is black and most 4.2 has a green block, that has been what I have always ran into. I had bought a a&m 4.2 but when I tore it down it was a 3.7 I had bought it cause I needed a 4.2 cylinder and the cylinder was different only by bore and the carb block other wise it lookes the same.