71 Dart 410 stroker ..

i drilled out the broken bolt...get tap out and tap it for a heil coil....heil coil screws up....something wrong .......had to pulled heil coil out....run tap again....put new heil coil in again...again...the bolt will not screw into heil coil....put it out......used drill bit again....and........hello cylinder ...i see daylight.