Unfortunately my little camera does not take a good usable close up, so will try to respond as best I can.
If I understand correctly, sounds like the bolt heads of your head are recessed 'possibly' down into the mounting hole areas. In looking at mine, they
'appear' to be fully exposed and, not having removed one yet, '
seems' to have a slight over-sized thick washer beneath the head. Thusly, sounds ... based on your analysis ... that it is a 11mm version .
But understanding that it is critical, I recognize that the only way to tell is to remove a bolt for inspection. So looks like I'm gonna go to our local NAPA or KRAGEN to see if I can get a 12-point
('triple square') socket that will fit.
I posted last nite this, so will re-ask somewhat differently.
If I remove #5 bolt, will that screw up anything by not being in numerical sequence. Read in Bentley that, during re-install, to follow a prescribed number sequence.
Then, to restate last posting, in removing this bolt, am I loosening something inside the engine that will 'drop' down, etc.?
Thanks for all the help EVERYONE !!!
Am embarrassed to be so stupid among all this knowledge.
ok, here we go.
the 12mm head has pockets machined in the casting so the bolts sit lower in the head, you can see that in this pic
look at the center front bolt hole, see how it is cut down into the head casting?
the washer will sit below the lip machined into the casting.
the 11mm heads do not have the bolt holes machined deeper like this, so the washer and bolt head will sit on top of the casting.
the pic you posted looks like the washer is sitting on top of the casting, not in a pocket machined in it.
so I believe that you have an 11mm head that had gasser head bolts installed in it during a rebuild(which would account for the triple square bolt heads)