Well, the mystery is starting to become solved. The front outlet on my head is about twice the size of the rear outlet. When both ports are used with a dual outlet manifold, the ports are the same size. So if I had a dual port manifold, it wouldn't be large enough on the front port to cover the opening. I'm pretty sure that my head is not a WD-45 head so it now appears that Allis Chalmers changed the head sometime during the WD production to change the front port size and stop using the rear port. I thought that happened only with the WD-45 and D-17. Part of my confusion is that I rebuilt a WD a couple of years ago that had the dual port manifold like my WC. I sold that tractor and later bought my current WD. When I went to put this one together, I had only the single port manifold (don't ask why I didn't notice this when I took it apart). So it now appears that the manifold that I have is correct and a dual port manifold will not work at all! I'll be able to confirm this weekend when I get back to the tractor as I have my old cracked dual port head from my previous WD for compariason of dimensions. By the way, my serial on the first WD was 59009. The current one is 101764. It looks like they made the switch to single outlet somewhere between the two serial numbers. If I'd purchased a WD parts book, it might have showed these details without question. Or maybe the head, water manifold and water pump came from a still newer WD. Anyone out there have a WD parts book which shows the complete answer?
Thanks to everyone that responded to my message. You guys are great!