Save the big bores for the X, R, & Ritter blocks. OE 340 blocks are thin. .030 is considered safe. Any bigger should be checked. Personally, I wouldn't go any larger than needed, unless there was a real reason. They aren't making anymore and I don't want to use it up with one overbore.

2 bolt mains and stock caps aren't the weak point. 550 to 600 is about the safe limit. Early 360s can go to 340 size bores.