Dude
100 ft lbs ??? my manual for a 92 Metro says the Camshaft housing bolts are torqued to 97 in lbs ( that's about 8 ft lbs )
Do you have a set of screw extractors ? If you have a steady hand, you can drill down into the center of the broken piece and insert a screw extractor and carefully wind it out ..... they usually work pretty good for me.
Good luck ...