Yep. That's correct. A rectangular-shaped, sheet-metal baffle plate is mounted inside the block through these holes. I just installed mine last week. Page 8-29 of my '58 Shop Manual says "Check to see that the crankcase ventilator baffle (attached to the block at crankcase breather hole) is not damaged and is securely bolted in place. Turn the crankshaft to see that the camshaft lobes clear the baffle".

To install the baffle, you will need to remove the oil pan and flip the engine over. The baffle slides between the cam shaft and the block.