4x4 conversion

okay, ive seen a few threads about 4x4 conversion, but i need more deatil. First off i want to converta 78 gmc sierra grande 1500 with a 350 i believe. I want to know how i would go about doing this, i understand that picking up a 4x4 a simply swapping out some parts would work. If so i would like to know what parts, and what models and years of vehicles i could use to do this. Any information would be greatly appreciated.

-Thanks