Do you plan to relocate the entire donor truck, or just scavenge parts off it? If you're collecting parts, be sure and get all the shift controls, wiring, etc. to complete the job. Also get at least the section of the driveshaft that attaches to the Ford rear end, as you'll probably have to fabricate a driveline to make the swap work. If he's scrapping the truck out, I'd suggest taking the whole driveshaft assembly from the transmission back, hanger bearing and all, and possibly the crossmember the hanger bearing bolts onto, if possible. On a swap, it's always good to have more parts to choose from than you need, instead of having to scavenge up bits & pieces.
I went the other way a while back, fitting a GM 14-bolt axle to a Ford F-350 with a trashed-out rear end. It was not a 2-speed, but the conversion had some interesting challenges such as parking brake and brake line adaptations.
Look at the final drive ratios for both axles, particularly the high range of the 2-speed. You might not be doing yourself any favors speed-wise unless the 2-speed has a higher-speed upper ratio.
Jerry
