You can use a 23/32 inch drill per the chart you linked without using a taper reamer. Cast iron cuts pretty easily with a tap, so you shouldn't have any issues.
You should use a 1/2 inch National Pipe Thread tap for your 1/2 inch plug.
If it's easier, use intermediate size drills. Not essential, but might be easier for you. Again, cast iron cuts pretty easily.
If the engine is not torn down so you can clean the chips out, you can fill the drill and tap flutes with grease to catch the cuttings.
Last edited by klhansen; 10/28/2019 3:14 AM.
