Be aware the liability difference between recovery on private vs. public land.
On public land the government has zero liability if you get hurt, and has few concerns with removal (other than to protect the habitat). You should ask permission, but if the legal title is clear you have the same right as any owner's agent to recover the vehicle (you do not need explicit permission on a public right of way).
On private land the owner's legal council (if asked for a position) may raise liability concerns, and prevent you from recovering the vehicle. The owner may want to see liability insurance to cover your effort (like the insurance a towing company carries).
These concerns are after legal title is resolved (determined stolen, and/or after the insurance company or owner releases interest). You do not want to risk possession of stolen property (even if it's a good deed).
The SBNF OHV-Volunteer group I am involved with has recovered over forty vehicles in the SBNF in the last ten years. Almost all have been reported stolen (all but the few found with dry occupants still inside the vehicle), and legal title (and other investigation) had to be cleared first.
In some cases the insurance company offered to pay for the recovery, up to a budget limit, and in a few cases they traded ownership for the recovery. Most of the older vehicles were simply documented and junked/scrapped. A few ATV's had to be airlifted out due to rough terrain (read, very expensive). A few folks are driving recovered vehicles, legally.
The expedient (but not completely legal) option is to determine legal title/status (or not) and then recover the vehicle (before anyone stops you due to other concerns). Document what you found before you started: the photos, a daily work log or report, and efforts to start the legal process (document the parallel good faith effort).
You may have to release the vehicle to the insurance company or owner, and receive zero compensation (other than a good feeling for cleaning up the potential damage the hulk could cause our sport). Giving up the vehicle is the risk you take by not working through all the proper channels (but it eliminates all the other problems, including owner awareness that could close the area to future recreation).
Good luck.
