I've looked at over a hundred engines for sale over the past year for a 1971 slant six, and not one of them was a 1971. What's going on with 1971 engines? Alot of them were made, but none exist today for sale....
That's strange for sure. If you are looking for a specific year, I would suggest a Parts Wanted ad instead of relying on other's sale ads which haven't been working in your favor.