ID 2 bolt main vs 4 bolt main???

Can anyone tell me how to tell if I have a 2 bolt main or a 4 bolt main without removing my oil pan? Chevy 350.

Thanks,
Dave

There really is no way to tell. The blocks have identical castings, therefore, identical casting numbers. Numbers 460703 and 10036033 are the only normal production blocks that were all 4 bolt mains. I've never seen any blocks with the first number, but the latter is fairly common as it is the block used in the Goodwrench crate motors. It is a Mexico cast block and not as good as the earlier blocks. 3970010 is the most common casting number, but can be either a 2 or 4 bolt main block. The 4 bolt blocks of that casting number are desirable because some were used in factory high performance motors such as the 375 hp LT1 350 as well as in trucks.