1971-1972 2wd to 4wd Conversion

[Duramax605]

I am looking to convert a 1971 longhorn to 4wd. Now i know most people will say to switch out the frame for a 4x4 frame but cant do that. Chevy NEVER made a 4x4 longhorn from the factory. (Actually called GM and cost me $75 for them to research all vins in that year). How difficult is this and what will i need other than the obvious 4x4 parts (transfer case, i have np205 already bolted to a np203 drive, new transmission, front leaves). This will be my first project and i'm already working on it as you can see with the transfer case. I also have a motor which should feel at home in the truck (motor that came out was a 400 sbc) I have a 406 to go in with dual predator carbs and about 3000 into the bottom end. Any help would be greatly appreciated thanks in advance guys!!! CHEVY POWER