Does any one know the significance of the numbers 340 4 or 340 6 on the side of a 340 block? had 2 340 blocks one had 340 4 on the side of the block the other had 340 6. What does the 4 and 6 represent? 4 barrel, 6 barrel? Also the 340 6 block has a blank vin area, (replacement block?).