I would go that route.
Drop the CATS and try to extract with a stud remover.
Then, use a TAP to assure the holes are accurate.
I can't stress enough the importance of the tap.

If you don't use a tap, a few things can happen:

1) Cross threading.

2) Jamming - whereas only 4 or 5 threads take hold then the stud jams
in the manifold.

You gotta chase the threads with a tap.

 

I have two studs that broke off in my left manifold. I was able to get all the others out with heat and replace them with new ones. The two that broke off I drilled through and just used bolts. Worked like a champ.

 

Did you use some kind of stud remover in conjunction with heating it up?

 

Take the manifold off and take it to exhaust shop to remove the studs and retap it. They will also give you the right size studs. This is what I did with my D1 and it costed my 30 dollars. On my 04 d2 exhaust shop broke the studs and gave me the car,without telling me. Just out of the shop my ultra gauge gave me pending codes related to oxygen sensors when I got home I noticed that he broke 2 studs to make the story short, it costed me over 200 dollars to fix this one. As far as studs are concerned, you can get them from dealer or get ford truck studs from autozone, slightly longer but worked just fine.