On just a mild build for a street car that won't see any hard track or street use, the block numbers don't mean near as much as the quality of the machine work and parts that go into it!!!! Over the years, I'd guess I've had more 2 bolt main blocks then 4, and have yet to have a block go bad---well, except maybe for a rod or two getting loose and making an extra hole---but even then, it was no fault of the block....