I have "Heard" of a similar thing that there was a run of years where the blocks were weaker....but don't know the details.
No matter what could he get a Stud Girdle to bolt on his small block chevy 2 bolt if he wasn't confident in it? Either that or get the block machined for splayed aftermarket mains...which I'm sure would be pricy and overkill on street! Just a couple of suggestions if he's really worried about his block. Anything can be done if you want to pay for it!