This is not true. A 2 bolt main will work like any other. Having worked in machine shops building engines of all sorts, I have seen more 4 bolt blocks broken then I have 2 bolts(theres 2 more holes drilled in each main saddle), not saying the 4 bolts are not good, but there is nothing wrong with a 2 bolt block. And I have never seen a difference between a 1/2t engine and a 1t engine as far as compression goes. The major differences in them were the heads. "SOME" HD engines had smaller intake valves and sodium filled exhaust valves.
So if you find a 5.7 in good running condition, dont be too worried about the main bolt thing.