...there is really no alternative to calling the cops at this point. Whoever chopped the vin number off, whoever borrowed the car from its original owner--they are strangely the one who doesn't need to worry about going to jail (the statute of limitations has long run out). But the timer starts now for whoever is in possession of the car--meaning, a resale, chop shop parts for sale, or hiding the car would represent a brand new crime.
At least, lets hope the new owner didn't pay Gas Monkey style (with a big pile of cash...)...Lee