Has the block been pressure tested to see just how long the cracks are? Sometimes the leak will extend beyond the visible part of the crack. I've done several stitching jobs with ordinary taps and steel bolts, but the cast iron plugs are better- - - -less expansion difference due to heat.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!