I am not even sure if they manufactured a 243...a 244 was the smallest I knew of personally. I think the smallest quick-tach grain head was 10 feet......but I never did even see one.
The 243 corn head is not the same as the forage row crop head that you discribed. The 243 head uses the same parts as the larger cornheads and is used to make high moisture ear corn when you run it through a screen on the chopper. Yes, it would be too narrow to use on combine.