Here's some pictures of the 3 different pumps. I have no affiliation with this ebayer, but I think it is the cleanest way to see the differences. There's also a really inexpensive one that has the bigger gussets, kinda looks like the medium duty, but it is made out of aluminum and therefore very light duty. Keep in mind I am no expert, I could be totally wrong. Would love any feedback - P.S. - on my previous post, I said the light duty water pump is for "manual power steering". I meant to say "no power steering"
heavy duty.jpg
medium duty.jpg
light duty.jpg