PnP does at least have a guarantee on parts you buy from them, if they are busted you can bring them back for exchange.

IMHO getting the engine from a car that looks like it was running when it was crashed is a great bet. Never hurts to poke around the cabin and look for oil change records, etc. This can also tell you how long the car has been off the road. Looking at the interior will also give you an idea of how well the PO took care of the car... IMHO if you come across a well crashed, but fairly clean interior wise car it's likely the motor is workable.

-Jason

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.