Good luck with M/T. And honestly, I'm amazed you're sticking with it. Most people have sold projects with less problems.
I can't believe your torque converter worked loose, those bolts very rarely come loose. I guess it's possible that the converter came loose and took out the flexplate which would then cause engine issues. It is surprising that you had transmission issues at relatively lower power levels. But whenever you exceed factory power levels, it's all a gamble as to what will hold up and what won't.