What happened to the 71 head? I personally am not a fan of the small, early logs. That's where all the dog log stuff came from. Ford improved the cylinder head in the 70's. The best, I think, is the last log they made. Except for the '70 170 small chambered head with the large flat top log. Cars got heavier with more accessories and Ford improved the heads for more power. The late model 200 and 250 heads have larger 62cc chambers. That's why the smaller 170 is preferred but hard to find. The larger chambered heads can be milled down.