Oil Pump Question

[Conaway2]

I’m rebuilding 2 oil pumps and have noticed several differences. One pump, which I believe is a newer one (according to the service manual) has 4 ribs on the body, a smaller discharge hole and the shield over the screen is held in place by 2 screws. The other pump has a smooth shaft, a larger discharge hole and no screws holding the shield on. In fact, it;s not clear to me how the shield is held in place - was there some sort of clip ??

Many thanks -
JIm