Traditional header bolts are what would normally have a 7/16" head on them, but for clearance, have 3/8" heads on them. However, if you are using an 11 mm, then you have a 7/16" head on your header bolts. That's gonna make accessing them a pain, too, although the 7/16" ignition wrench makes it easier. You might want to break down and spend $15 and get a set of ARP header bolts.
Either way, buy the set of ignition wrenches. What's funny is that they have added those to their 200 piece tool sets forever, and hardly anyone ever uses them. Almost every time I turn someone on to this little header bolt tool trick, the other person slaps their forehead and tells me they've had a set of those wrenches for years, and never knew what to use them for. lol.
There are very few things in this world that are as rewarding as the feeling you get when you suddenly discover the "right tool" for a PITA job.
Take care,
~Chris