We always replace the drive in plugs with 1/4 NPT screw in plugs. The holes are the right size for the tap threads. We have always down ours as part of the rebuild prior to hot tanking so I have not done one on a running engine.
However, I believe that with a little care metal shavings can be kept out of the engine.
Threaded plugs won't blow out like the drive in ones so it might be worth installing the pipe plugs.
If you want to go back with drive in plugs, I will mail you three for a buck, (US).
Jim
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