This is documented in the 64-65 Mustang Chassis Assembly manual. The hardware part numbers, direction of the bolts and the location of the washer.
I recommend you get a set for your car's year, plus the 64-65 Chassis Manual.
Of course, you could look in the Library section of this forum, under topic "Mustang Hardware Spreadsheet 64-66", in file "MHW64-66AP02.xls". It's sorted by application. Be advised that the application is "Engine Mount, Rear, . . . ". That's Ford's description of the rear transmission mount.
Jim