my dad bothced the winterizing on his merc 5.0, crackblock on both sides ,,, can it be saved, only 40 hrs (cracks are hair line only about 3" and no water in the oil. starts fine)

nope, once their cracked their pretty much done. Does water come out an into the bilge?

yes , the water dumps inro the bilge

I just had a guy last night tell me he used JB Weld with the identical problem. He said it held up great.
Are you sure there is no crack on the inside. Is the oil turning to milkshake color after running it? It will start fine with water in it.
I know theres a weld shop that says they can weld blocks and they guarantee it to.

Agreed. Why even risk it?

Scrap Iron now.