I do have a tool to install plugs with the engine installed.
Consists of a bent handle/shaft with a ball socket on the end.
The socket is threaded and there are several ends that screw on it to fit the plug being driven.
This is a commercially available tool, I'll look Saturday in my tools and see if there is a Mfg. # and name.
I have used it several times and never had a problem installing or after installing.
In my "L" I installed several Marine Brass plugs when I discovered the original steel ones were rusted away, leaving only mud sealing the hole.
I cleaned out the mud, using a bent hanger, and then flushed the block with Battery Acid. Don't ask why, seemed right at the time...
It did clean up the inside of the water jacket as far as I could see, and after the plug went in, there were no more problems.
When parked, the "L" had over 500,000 miles on it and still ran great, never had the heads off, had cold air and went thru 3 transmissions.
Been parked since 1987, drive it onto the trailer to bring it our to Mena in 1996 or so nd it hasn't run since, low frozen.
Hope to get to it this year or sell it...
Ray