How do I get these bolts out?

[BP]

I probably would've used vise grips to break them loose and hopefully walk them out with my fingers, then throw that garbage in the trash and reinstall some ARP header bolts for $15.00. Or $30 if you want the stainless 12 point ones.

[Chili]

You're funny. To get full amount of leverage on rusty header bolts a cut down Allen is the correct tool. Ball end hex drivers should be in your toolbox but in your scenario may not give you the full contact inside the Allen head that you may require.

I know that the ones I can access were fairly easy to move, so I'll keep the modification suggestions in mind in case I have trouble..

[Chili]

I probably would've used vise grips to break them loose and hopefully walk them out with my fingers, then throw that garbage in the trash and reinstall some ARP header bolts for $15.00. Or $30 if you want the stainless 12 point ones.

They're all over on this engine too.. In that first pic you can see the thermostat housing uses them, and you can even see one on the opposite side of the valley.