I want to remove my pedal box so I can swap it over for a Non servo one. I've hit a wall though as no matter what I try I can't get the damn security bolt things out holding it up on the dash rail

I've tried grinding the sides down to get my bolt gripping doo dah sockets, mole grips etc I'm thinking of using a cutting disc to put a slot in and try a screwdriver? Anyone know what thread/size the bolts are so I can get replacements?
Thanks