I Called ARP today.. and this is what they told me.... The b16 and b18c1 head bolts are pretty much identical..both 11mm and only off in length by the thousands.he said it would be just fine using my b18c1 arp head studs for my b16top/b18c bottom.(woohoo).and i ask them about the washers because i have a gsr arp head stud kit that came with the main stuid kit as well was missing 3 washers for the head studs..i asked to order the 3 missing washer and he just reccomended i bought them locally..saying that the oem washers would be just fine.its the head studs that are the real difference... for anyone else that was wondering...