EGR holes one back of head, best way to plug em?

Go to your local machine shop and ask for threaded inserts. The holes in the back of the head are the same as a couple in the front of the head where the long threaded studs are installed to hold your a/c ,p/s brackets. They should know what you are talking about.
 
I just cut the ends off of the smog tube and flipped them around and bolted them back on.Free,took about 5 minutes,no problems.If the heads were off the car I would've used plugs,but,since they were still on,my idea worked best for me.Good luck.