I looked at a 270 yesterday. It was a later one with the later GMC valve cover letters and a 6 bolt fly wheel. The casting number on the bell housing was 3837001. The number would be hidden if there is a transmission because the number is in an indentation on that surface. This one has angled flats on the bottom of each side for the motor mounts. So there has to be at least one more number for the older style with side mounts. Both will have the floor starter bolt holes and both will work for you and take at least an 11" clutch.
