I was in the same boat with my truck a few years back. old pink, bill of sale. had the vin signed off by an officer buddy, weighed it an filled out some thing about why its been off the road. Done. no big deal. Consider yourself fortunate. A friend is having alot of trouble clearing a car with no papers.
Stamp the Vin into the firewall? Say thats what was there when you got it? My truck had the vin on a tag on the firewall, but its a ford.