I am told that drilling for four bolt mains will actually weaken the block.
I have a set of Milodon caps and am considering just line boring and using the two bolt configuration on my next deal.
Casting number says 71-73 340 block.
I would have the block sonic tested before I decided how large to bore it.......especially if you want to really open it up.
I wouldn't sweat .030 over , but if you want to open it up , better to know how much meat you have there.
Stroking is the best way to add inches to my way of thinking.