Rounded off an exhaust header bolt.
The 2 outside ones loosened fine, the 2 inside ones just courteously changed their shape when I turned the allenkey.

2 Questions...

1. What's my best option for loosening? I've thought of...

-Filing flats on the bolt heads, not easy.
-Sawing bolt head in half and using a screwdriver/bit with ratchet.
-Drilling into the bolt, ..

2. Do I need specific bolts? they have a very deep head on them. can I use regular allen bolts?

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PCV REPLACEMENT ECU WITH 04 WIRING LOOM STAGE1&2DNA GEL SEAT INSERT LOWERED 20mm FRONT+REAR CLUTCH ARM MOD
FORKSPRING SPACERS TALLER SCREEN THROTTLE GRIP CAM MOD DISTANZIAS 46TOOTH REAR SPRKT
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...SHEEPSKIN - Because a pain at the rear is not just a moany pillion.