This does not look like a bolt I have seen concerning the head.
Without some kind of measuring tool/object (dollar bill, old tennis shoe, yard stick,
etc) next to it, it's hard to even guess where it might go. ..
Bolts like this (8mm coarse thread, thin-head) were used to attach the engine transmission spacers on some engines. They like this one I just bought from Fred S here on the BB. The recessed holes on the right under the starter hole use thin-head bolts.