The shops around you won't do it? They're lazy and looking for easy jobs that pay well. Drilling out manifold bolts sucks, but it's work that needs to be done. The problem is that it can go sideways and completely eat your lunch. This is a job that's incredibly difficult for a novice, but gets significantly easier with practice.
You can do it yourself, and an EZ-Out is the correct way to do it. Center punch the bolt before you start drilling. Keep your drill centered and straight. Drill deep enough to fully seat the EZ-Out.
Take the time to set yourself up for success. You must get the drill straight and keep the bit centered on your bolt. If you get sideways or wander you'll be in the threads in the block. Take care with that EZ-Out! If you break it off in the hole you're really between a rock and a hard place.
If there's any thread sticking out on the bolt, a better solution would be to thread a nut onto those threads and weld it on. The heat will help loosen the bolt and you can put far more torque on the welded nut than you can on an EZ-Out.
