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.