It is not rocket science to install gears but it does require some special tools and knowledge. Trying to explain it over the web is futile at best. It is not for the average do-it-yourselfer. You could try to find axles from a F250 but then you would have to use 8-lug wheels.

Personally I do not think a swap from 3.55 to 4.10 (that is the shortest gear you will likely find in a donor) is going to do much for you. That 5.0L needs gears to get moving. The larger the tire, the shorter the gear you need. I have recommended 4.56s to you and others with similar combos before. When it comes to gears go big or go home.