I assume by your username that your blazer is a 90. The first thing I'd do it find out what transfer case it's got, then I'd find out if anyone makes a part time conversion kit for it. Sometime in the late 70's GM started using it's own front axle, which is the 10 bolt, not a Dana 44. If you've got a 44 that you're going to swap in, just buy a set of of manual locking hubs and you should be good to go.
A broken 84 k5 and lots of mud, it sucks to be me