I’m done. here’s what I did:
not sure I mentioned it, but tried LH drill bits. no luck.
to recap: broke bolt extractors twice in the bolt. the last time, I used tungsten carbide cutting rotary tool bit until it wouldn’t reach in because of the angle anymore. had to get a tungsten carbide “ball” cutting bit. for some reason, craftsman doesn’t make the long cutting bit with a rounded end. anyways, had to mash that ball cutter around a long time until finally broke through the extractor chunks (the hole was otherwise through the bolt).
at that point, I could have tried another extractor, doing it even better, or drilling a clean hole for the "plain bolt’ soution. but I had an M8-1.25 tap and corresponding drill bit (17/64-inch, or 6.74688mm), sears combo set, on hand. first time ever tapping a hole. figured the next step after that if it fails is to make a clean hole.
long story short, managed to get the hole re-tapped. cleaned the other one too. worked great. unfortunately, angle is off by maybe 5 degrees on the damaged hole that is the subject of this thread. it was fun to tap!
anyways, problem solved - apparently - actually, I’ll have to report back about how the transmission mount - that’s what this piece is, basically - hangs to the car in the long run.