I think it is a year thing. I originally bought a long water pump for my 350 because it is a 99 engine, but it was too long to clear my electric fan. So I ordered an earlier water pump setup and it is the short one. I don't have my Summit catalog here to get the exact years for you, but the short ones were used like in the 70's, I think, then the long ones came on the scene.

Someone else might be able to give you more definitive info.

Don