I repair these stripped late model evo manifolds every day.. Its not for the faint hearted, as the studs will not normally screw out of the manifold, even after heating the manifold with the oxy. So, I have a go first at removing them. Next, you have to drill them out. This is a very difficult and laborious job, as the studs have become SUPER hard and crystalline with repeated hi temp heat cycles. If you are skilled, you will be able to centre the drill and then retap the hole. I can usually do this, but I helicoil them any way.
The thread is 10 x 1.25 . I try and use the genuine Mitsi studs ( expensive), but any exhaust shop should have the equivalent in stock. The Mitsi studs are the most reliable ( complete with their washers and nuts).
The Secondary Air System ( not EGR) threads are 16 x 1.5. It is very easy to source these bolts from a good nuts/bolts shop.
Good luck in drilling the studs.. you will need it. Remember, VERY slow speed with drill, and resharpen the bit every minute or so, or when you hear it squealing. The crystalline hard studs are a killer of drill bits !!!!
