These help-
Cupped washers for chain tensioner
So did this-
Skate wheel tensioner mod
Those were band-aides for the original type. I have used the four bolt bracket with no mods, except the skate wheel.
I have drilled the chain stay with no problems after hundreds of miles. I sold the bike, and have not heard anything from the guy, and I told him to call me if ANYTHING went wrong with the bike.