Head bolt nuts

[STeeL25T]

Probably asked a million times, but I finally got a friend to bring a 250 ft lbs impact for my cam gears, that wouldn't break it lose. Called yet ANOTHER friend with 500 lbs one, got it of and pull the cams out, thinking I was about to finally pull one of the heads off but I can't get the head bolts off. Looks to be more than a 12 point bolt, we didn't have a impact socket that would fit but we gently tried to use a normal socket and that wouldn't break it lose. What should I be using to remove these last few bolts?