Those bolts are really tough. I doubt you will break one off. I wouldn't hesitate to hit the wrench or breaker bar with a hammer to loosten it. Again, be sure you are turning it the correct way to loosten. If you are on the outside looking at it from the bottom not the bolt head size it needs to go clockwise to loosten it.

Good luck.

tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.