'77 Ford F350 2WD to 4WD conversion

I own a '77 Ford F350 2WD dually singlecab flatbed. It's all original and is my families old farm truck. I want to convert it to 4X4. I have all the tools and mechanical know how.
   I have two questions; first is there any company that makes a 2WD to 4WD conversion kit for my truck?
   My second question; I live in South Central Texas. I would like to find a donor 4WD truck in Texas. It doesn't need any body panels or engine. Mostly I am looking for a frame, trans/t-case, axles and etc parts. the cheaper the better but any truck will be considered. I own a '99 Chevy 3/4 extended cab 8' ft bed 4X4 w/ bad motor. Will consider trading for equal value truck.