DMV fees and past due loans aren't the end of the world. #1 no one has said this truck is stolen. Usually the lending company is happy to get anything out of a deal like this. It was the previous person who screwed the pooch here.
Find out who the lean holder is. Tell them what happened and see if they let you buy out the lean at a reduced rate. Often they will take a fraction of what's owed, especially on a vehicle this old.
Like I said earlier, DMV can work with you too. My 4runner had lots of back fees when I bought it through a lean sale and they were able to waive most of the fees. They saved me around $500. Many DMV employees don't want to take the time to do this, but it can be done.
Even if you save $500 total, you've got a clean '91 for $2500. That's not a bad deal.