Rusty, Todd, et al, It's your engine, but I would suggest that you remove that rear plate to do the drilling and tapping. It would be a darn shame to leave one chip in the oil system and scrap a new motor. I had to take apart 30 air cylinders once when I had to drill and tap them and chips still showed up in the cylinder no matter the precautions I took. But, if you must do this while the motor is assembled, pack the hole with heavy grease when doing the tapping. Taps tend to push the chips in front of them.

Rick Girard