I am just finishing up my rebuild on a 4401 and I have been having a hell of a time finding info and parts on this case. I called the dealer this morning to try and find a speed sensor ring on the output shaft and it's been discontinued. I asked him why I was having so much trouble when the case was used for so many different years and he said they weren't breaking down often enough for people to work on them. I imagine most people aren't tearing it up off road in a 3500 like they do in the 1500s but still. I don't know if that helps.
The shift fork on mine wore out and it was stuck in 4 low, when I took it apart everything else was in really good condition, like almost new. 215k on the truck and it was used primarily to haul a big boat and a gooseneck camper before I bought it and I use to to haul my slide in camper and raft trailer around the mountains of Colorado. It's been ridden hard and aside from the fork it's in really good shape. I replaced the seals and bearings, the fork and shift hub and I'm right around $200. Don't jack up that speed sensor ring if you tear into it though, even ebay doesn't have it. I did scar mine but I'm going to have to clean it up and reuse it. I don't know anything about the other case you mention but thought my experience with this one might help. Good luck on your build.