In my opinion, I don't know his buddy would be happy to see his rig sold. Otherwise his buddy would have sold it himself and kept the money. His buddy was doing him a favor by giving him the truck to use and one possible reason that he did so was because he wanted the truck to go to a good home since he probably has some time and money keeping it up. Selling a rig that was giving to you could be considered an insult.

It may be questionable whether converting a 2WD to 4WD is worth it, but consider the cost of a good 4WD rig in good shape and it could possibly add up to the total cost of the conversion, $2500-3500. In other words, it could easy be a wash either way, considering the rig was free. A lot depends on just how good of shape the rig is. Consider in the end, the only part of the original rig you'll have left is the frame, body and engine. Everything else will be swapped out with different parts. Also, who will do the labor. If you have pay someone to do the labor, that will make the project a lot less cost effective, as opposed to if you can or know someone who can weld and do the work for free.

You should look up Elbow Grease on this forum as he's done the conversion and can actually comment on whether it's worth it or not. One major advantage of converting a 2WD truck to 4WD and SASing it is that the front frame rails are more suited for a solid front axle and you can run a safe minimal lift, which means that you can keep your tire size as small as 31" and the lift as low as a stock 4x4 truck if you want a more streetable rig.

Just my opinion. Good luck.