I would recommend talking to your dealer about making the 1183 cornhead work. It can be and has been done I have seen, but can't tell you what specifically is involved. The 800 AGCO head may or may not fit without modification. There were 2 versions that you can look for. Check the serial plate on the header, located on the left side of the head. If it is an 800C model, that means it is made to fit the Gleaner and MF conventional combines, which have the same feeder hook-up as your 8780XP, and so it will hook right up. You may have to change a few plates for filling in the width difference, and since yours has lateral tilt, the upper beam of the header may have to be moved, which is done with bolts and pre-drilled holes, so no cutting or welding. If it is a straight 800 head, then it is made for the Gleaner rotary. The header frame is made so that your MF will hook up to it, and the feeder opening can be easily adapted to fit your Massey, but the auger will be different. But you can simply remove some of the retractable fingers I would think, and cut some of the flighting to make it match the 8780XP, rather than buying a new auger through AGCO for it. I've had to change some of these back and forth from lateral tilt to non and once from the 800C on a conventional to the Gleaner rotary before when a neighbor wanted to use the head we had on a C62 on his R62.