the D1ZZ B is the correct part number for the boss 351 head. But the D1ZE B casting number is for the boss 302 replacement heads ,dont let the casting number and the parts numbers confuse you. yes alot of the times the casting number and the parts numbers coinside with each other BUT NOT all the time remember ford was going to build the boss 302 into the 71 model year. most of the books have the D1ZE B head listed as a Boss 351 which is wrong. either out of confusion with the actaul part number , or because they didnt build any boss 302 for sale to the public. Of all the true Boss 351 heads i have seen , have all been D1AE GA ,I have not my any means seen them all , but i have seen probably 25 set , yes a small percentage, but still a fair amount.I would say if there was any other casting number for the boss 351 heads i would say it would be the D0AE N . but you must remember that Ford listed the combustion chamber space for the Boss 351 as 67cc, which is what the D1AE GA heads had , and the D0AE N heads as 63 cc , just food for thought.