What Is It Called?…Nothing Will Fit It?

I almost have the heater box out of the aspen third heater core I have worked on this week. This bracket is a real pain in my ass. Notice the center bolts I have tried Metric and Standard nothing seems to fit them. It has to come out I cant slide it threw the fire wall because the sides over lap the fire wall edges as in shaped as a T. Only thing left holding the complete heater box in. Any ideas?. Thank You. :cussing:
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Author: Mopar_Gods