Bigger head studs than stock?

[No disintegrations]

No and I see what you are saying. If you look in the water jacket where the bolts go in though you will see there is a limited amount of iron between the the head to deck surface. The fasteners pull up on that and will distort some amount and you reach a point of diminishing returns. Or pulled out threads from too much tension.

 

[Mike T]

Been doing a little experimenting with mock 7/16 x 14 bolt holes. Stepping up drill sizes gradually to larger tap.

If you were to go to a specialty thread 12mm x 1.5 is larger than 7/16 and the block seems to have enough material for proper thread engagement. A 27/64 bit required for 1/2 x 13 leaves just a hint of the original threads and would tap very well.

If for nothing more I could see going 1/2 to save a damaged block...seems to be less intrusive than a time sert.