After thinking I take that
oil passage comment back, Some of the very early 406's were 390HP blocks carried over and bored to 4.13 sorry for the mixup. The one crossbolted 406 I saw was a C2AE-6015-BD and was rumored to be one of a small batch Ford cast and approved for NASCAR. The 406 is a weird block and had six versions cast in the year they were used. As the horsepower wars raged on Ford was upgrading them to compete in racing. It's kind of a tweener between the 390HP and early 427's and was ever changing to be better. As the 406's were blowing up on track the 427 was being developed and the 406 was the test mule for these changes. The rest as we know with the introduction of the 427 is history. G.