[craggle]

Looking at the photos again I reckon that is a repair.

Cylinder head bolts are meant to be hex head bolts but the one in that corner looks like a socket head cap screw. I reckon the block cracked in that position, It was then welded up the re-tapped to a bigger size, Probably a metric thread.

Luckily the outer row of bolts are pointless anyway and can be left out, so as long as the material between the bolt hole and the cylinder liner is solid, you should be fine.

Craig.