there are 2 different head stud kits for the d16y and the d16z. they are 208-4305 and 208-4301 respectively. i ordered the z6 kit, thinking it would work with my z6 head, but when i tried to bolt it down, i found it didn't work.. when bolting up my y7 bottom to my z6 head, i found i needed the y7 kit with one of the (longer) bolts from the z6 kit. hense the z6 kit being screwed down, but never torqued. so i called ARP and ordered the replacement stud to complete this z6 kit FS.