The Dana 44 (manufactured by Dana) stopped being used somewhere in the late 70's as a front axle. 1980 was really the start of 10 bolt (manufactured by GM) front and rear axles in the K5 and K10. In a comparison with the front axles, you really can't compare them because they are practically the same. Most of the knuckle out parts are either the same or of equal strength. The gears/carrier/shafts/etc. have small differences between them but in the end I don't care who argues shaft thickness or spline count...it all feeds out to a tiny 297x sized u-joint period. If you don't break that part, you will snap the necked down part of the inner shafts regardless of it being a 10 bolt or D44. As far as a 12 bolt to 10 bolt comparison on the rearend, they are pretty much the same as well except for ring gear size. Being that the 12 bolt was never anything spectacular in a truck and the last one made is over 30 years old, a SF 14 bolt would be a wiser choice.
All of these domestic half ton axles if you plan on using them for doing anything other than driving on pavement or very light fourwheeling suck. The c clip rearend is inherently a bad design, has many weak points, and tough to deal with when it fails. Most also use a light duty 2 pinion diff which are weak and notorious for splitting apart when abused. Sure, you can throw lots of money at a better carrier, chromoly shafts, fancy ujoints, etc. but you will be time and money ahead upgrading to something better. I really only would consider a Ford 9" or a Chrysler 8.75" rearend because they have pressed bearings, removable centersections, and are very strong from the factory.
Unless you are going to keep this a street queen, I'd upgrade the rest of the driveline as well or atleast plan on spending money when something goes pop.