the block im going to put these heads on is a 390 block i had bored to 4.110 or .060 over, i have the book from Steve Christ that i am comparing these numbers to, so if the info is correct then these should fit on my block with no problems. this book has these casting numbers as 56.4-61.0 cc with 2.02 intake and 1.66 exhaust and port size of 2.34x1.34 on intake and says that late 406 has spring seat cups ,so i am taking it that since these are cast in the month of may, that they will not have the seat cups but all other specs are the same, this is what im seeking