How hard is it to convert a 2 wheel drive to 4 wheel drive usening the 2 wheel frame?

I have a 1970 chevy 2 wheel drive I would like to make it a 4 wheel drive. I have all the 4 wheel drive parts needed to do the job. I would like to use the 70 frame. how hard will it be to do this?|||quite a bit of custom fab work will be needed, like welding and sheet metal fabrication. Youre going to want to beef up the frame and create braces and mounts for the T case and the front suspension will have to be fabricated from scratch and everything needs to be plumb and true or else you will have weird handling and it could possibly tear itself apart if not done right.