Ok to the head off . Now i can see whats happening. The standard bolts are cap heads so there is no issues. With the ARP obviously they are atuds with nuts. The issue is that the opening for the bolt to go through is just enough to clear the cap head 16.8 mm.
A 11 mm socket OD is the same 16.8 mm so it clears but a 12 mm socket is 17.8
So eiather open her up which im not going to do as im not rebuilding the head. There would be aluminium shavings all over the place. So before anyone rebuilds their head DO THIS. Ill see what ARP can say = solution and at the same time talk to socket suppliers