This idea came up again at the GGP yesterday. Converting a 4x4 platform into a FWD gas + RWD electric is probably the easiest way to get a DIY hybrid. I know it's not exactly what you had in mind, but it's something to consider.
http://ecomodder.com/forum/showthrea...awd-12402.html
The F250 probably isn't a great platform for a two-mode hybrid. You'd need a really big motor to get it underway, and lots of (expensive, heavy) batteries to give it any kind of range.
However, if your goal is to improve the F250 any way you can, I think it would be great if you had a hybrid system with regenerative brakes and enough assist to allow you to go engine-off occasionally.
You should study the Tahoe/Yukon hybrid, which gets +6 EPA City MPG (+40%!) vs the Tahoe XFE. Maybe you could source some parts from it.