Water pump in '63 motor vs. '66 motor

I recently pulled the motor out of my mustang, and had to use it's pump for my new motor as it didn't have one. I was surprised that the old pump didn't fit the timing cover for my new motor. (1966) I thought I was pretty clever so I pulled the timing cover from my old motor, (1963) and just put it on the new block. Well when I put it all together and back in the car, it is leaking like crazy between the pump and the timing cover. I had a mechanic friend of mine over and he asked if I remembered to put the plate back in. I said 'what plate'. It didn't have one when I took it off. I have tried ordering a pump for this timing cover and it doesn't have a plate. However when I went to re-order the gasket, it asks if you want the pump to plate gasket, or the plate to block gasket. How can it have two gasket choices, but no pump with a plate on it. It took me a while, but I figured out from the code on the block that one was a 1963, and one was a 1966. So does anyone know why it is leaking so bad? Should I have a plate in there? I can't seem to find this plate, and the replacement pump doesn't seem to have a plate at all. Any help is greatly appreciated.