Don't over think it. IF he is the rightfull owner, then get a normal bill of sale from him stating your names, dates, description of vehicle, address and price. Or use a bill of sale form from the CODMV. The price may or may not mean anything to DMV because what this is all about is if someone comes along and proves it is their truck, they will get paid what they say it's worth up to $16000 or $8000 or maybe the truck. I know it won't happen but that is the procedure in most states. If you stick to truth and pay the money, you will sleep at night and be a better man.
HOWEVER:
In your unique situation where you know the history, you know that no one could prove ownership but you, you don't need to do anything or spend any money. Get a bill of sale and an affidavit from the brother in law. If you are going to fix it up and drive it, that takes years and money and plans change. If you are going to flip it as is, or sell it after fixing, you still don't need a title. Sell it on with a bill of sale. Take a pic of it on the farm and drag it home and stare at it, love it, admire it, clean it up and examine it.
