that is actually a marine block, I have had a few over the years, never seen a new one. the mains are not usually the problem . if you look at the side of the block it has extra ribs cast into it like a marine block which 1st run hemi's did not have. our s/s hemi engines back in the day with stock blocks used to split down the outside length roughly 1 1/2" to 2 " below the deck. this block should not have a problem, it also seems to have much thicker walls according to the sonic test. does it have a casting date? I would also install main studs and have it line honed.