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That looks like a Dana 44HD and the hubs look like they may be Warn hubs. I'm not 100% sure on the hubs but they look like mine and they are Warn hubs.
Definitely a Dana 44HD. The hub casting on a Dana 50 doesn't neck down back near the face of the wheel. It stays pretty much at that diameter out to the end.
Sorry for the bad picture, but the lower picture below shows the Dana 50 TTB hub on my '97 F-250HD CCSB. You can see how different it is from a Dana 44HD in the OPs first post.
I have Mile Markers on my F-250. I don't know what model number they are, but I've had them since just after I bought the truck in 2000 I think. They haven't posed any problems and engage properly everytime.
I'd recommend them.