Well after giving it a lot more thought today, I don't feel confident I can get the bolt out so I'm going to take it to a shop about a mile from my house. He said they can drill it out and install a heliocoil that will keep the hole in the same place and the same thread size. Probably cost me an arm and a leg, but owell.

I tried threading the various stainless steel bolts on the other side without the manifold on after making sure the threads were very clean. A few would thread just fine but some would start to bind up. I would then take it out and try the stock bolts, and no problem. Looks to me like the stainless steel is just too course for the soft aluminum so I'm going to look for some aluminum bolts. From my measurements, these are the ideal sizes needed for each of my Needswings manifolds:
(1) 140mm rear
(1) 115mm mid rear outside
(1) 125mm mid rear inside
(1) 105mm mid front outside
(1) 110mm mid front inside
(1) 90mm front

The middle ones are different sizes because the outside ones only have about 1/2" to thread.
The bolt thickness is 5mm. Now I just have to search to figure out how that translates into a bolt size (unless anyone has a quick answer).

One more question. If I install all the other bolts, do you think I would be ok driving it slowly a mile to the shop rather than towing?

Thanks everyone.