[Walt Fricke]

Drill small holes in the plugs and use a slide hammer with a screw end to pop them out.

I've always (that's twice) tapped the resultant holes and screwed in plugs. Be careful not to tap too deep or screw in too far - you need to look to see what connects to what so you don't inadvertently block something off.

I used aluminum plugs (weight, don't you know) the second time I did this, but found that I could not remove them, which was much of the purpose of using screw in plugs. So it will be back to brass plugs, which can take more unscrewing torque. Standard IPT taper threads and plugs.

And not all of the plugs need be pulled. Maybe three, as I recall.

Otherwise, you purchase new stock plugs and press them back in after cleaning.

Walt Fricke