That is TOTALLY WRONG!!!!!
Sure, the rest of the parts on that rig were in damn good condition. Everything: (axles, tranny, engine, xfercase, driveshafts, etc...)
BUT it is STEALING. Despite the fact that that rig was dumped in the woods, whethere it was stolen, or dumped by the owner, one can never know... IT IS STILL THEFT OF SOMETHING THAT ISN'T YOURS!!!!!
If you want to do it legally, you can call the police, let them know where it is, send in a VIN, and apply for a title. The process is FREE, and if nobody has reported it stolen after a certain period of time (30 Days in WA) then the vehicle becomes yours.
That is the right way to do it. If I EVER catch folks stealing parts off of "abannonded" rigs, I call the police.
It isn't yous, so don't mess with it.