Be very careful with the easy out. They are brittle like candy canes and very, very hard. If you break it off in there it will NOT drill out. Heat is your friend here, I will disagree with Ben above (he makes a great shifter!!) about the heating. Heat the surrounding head area to grow the hole larger not the bolt. Propane might not be hot enough but it is worth the try. Propane isn't hot enough to harm aluminum so heat for 2 min and try to loosen. Then addd 2 more min. Then let it cool down and start again. Do not heat with the easy out in there.
What size have you drilled it out to???
Do you have all of the other studs out already???
Stomski makes this kit for exactly this job:
https://www.stomskiracing.com/products/boxster-996-997-exhaust-bolt-repair-kit
