The 2040 A&B engines had a hex head plug
in that 2:00 o'clock location and the plug
was drilled and tapped for a drain petcock. Later engines didn't have the petcock installed, and in some cases the large drain plug was square headed.
Don't confuse the drain plug at 2:00 o'clock with the hex headed plug at 3:00 o'clock and further away from the filter, ahead of the oil
feed pipe. This plug is an oil
pressure relief valve.
Once you have the drain plug out of the block, you can usually drill and tap it and install a more easily used petcock, like the earlier engines.