Will be ok when all welded up as its only in the water galleries.

The welded up bit stops the water getting passed into the gasket.

When the block gets machined they make the old hole bigger so the new long studs can pass through and screw down into the new threads further down inside the block,therefore no pressure on the weled up area of the cracked bit.

Paul,

there are oil galleries but there at the side of these holes and are nothing to do with the bolt holes.