Derek, there is only one advantage to closed knuckle axles over open that I can see, is that they have kingpins instead of balljoints, which are a little more tough.
Downsides to closed knuckle: drum brakes only, external hubs (which arent desireable), smaller axleshafts, smaller ujoints at the knuckle, axle seals frequently go bad on these and make a mess. Also, closed knuckles cannot turn as tightly as open knuckles and therefore have a larger turning radius.
Open knuckled axles are pretty much the opposite. '70 models with drums can be converted to discs, otherwise all other years have discs to begin with. Most have internal hubs, but some still have external. These axles also have larger shafts and u joints, and dont have annoying tube end seals to make a mess. Also you get an improved turning radius.
The closed knuckle d44 in my truck was fine for DD duty (4 wheel drum power brakes) and light wheeling with my 32's, but since I plan on lifting my truck and getting bigger tires, the axle and those weeny little drums up front had to go. I would have gone to a newer d44 with open knuckles, but lucky for me I got a hella deal on a d60 for $150.
