I think the 1 bbl. integrated head was a hit and miss between 1975 and 1978. I had a '78 C10 that had a bolt-on intake head. It was in a light-duty emissions truck. Came with converter, but got lost after the warranty ran out. I have seen some '75 - '78s that had either setup, at least the trucks. Possibly they used whatever engine was available to throw at a 1/2 ton since all the heavy-duty (non-catalyst) 250s were non-integrated.
