Not uncommon when you push the boundaries.
That engine is still running I beam rods so it is not a full-on race engine but you have remember those engines were originally only built to run to 4,500 rpm but you can spin them up around 8,500+ rpm when you let them breath properly so they really shouldn't be bagged on.
It's an 010 4 bolt block but there were still plenty of them with core shift.
I found the best ones were cast in Mexico - very little core shift and even all the block threads for the head studs were chamferred.
You had to look for the "made in Mexico" in the casting near the distributor
I raced them successfully in power boats but not using any standard internals and with a roller cam and rev kit.
I acknowledge that you can make a Y block do the same thing but Chev parts are much cheaper and easier to get.
You can easily order a set of Chev Brodix aluminium heads, Ross pistons, Carillo or Eagle rods, Crower or Eagle crank, Isky roller cam etc at any race orientated auto parts store or website and for a lot less than the comparitive Y block parts would cost.