Might not be worth as much, but the slant 6's I have seen are bullet proof.
We had one in a Demolition Derby car one night. Got hit in the front and drove the radiator back into the fan. Later it got knocked up on a K Rail and busted the oil pan. Once we got it out to the pits we held the gas to the floor and tried to blow the engine, it would not blow. We left it red hot and went to get something to eat. Came back and hit the key to load it on the trailer, and it fired right up. It boarded the trailer under its own power and ran around the farm the next day.