5/16 wrenching header bolts

for some reason those heads look bigger than a 5/16 wrench....maybe a 7/16 wrench? I went to the arp website and they don't list the wrenching size for the mopar bolts. They do have a universal bolt kit with 5/16 wrenching but only in the 3/8 thread size. I sent an email to ARP requesting the info. Thanks for the help.