That's an unbelievably open ended question.
You'r probably going to be looking at an industrial diesel and modding it to get the HP up to a reasonable level. Lot's of people think about the Cummins 4BT, and I keep making the point that it's nearly 800lbs dry weight, let alone a tranny that can handle the torque. It'll make the weird weight distribution of a pickup that much worse. It's also almost 4L.
You could get a 2.0L-3.0L 4cylinder industrial diesel for a much more reasonable 4-500 lbs, and still somewhat cheap if you cruise Ebay or get lucky locally. Buy you're also going to be looking at an adapter plate.
VW diesels can work but the computers in them get really cranky when being transplanted and everything isn't just peachy perfect.
Others like the Mercedes swap have been done, and at the time of posting my reply, there is a diesel swap thread not too far down from this topic.
http://www.therangerstation.com/forums/showthread.php?t=22729
I'd start by studying the differences in the Diesel in your Chevy and Ford for small details.
What will the truck be used for? Will it be driven daily? Hard or soft? Mileage a concern? loooots of questions that need answers to.