[Sirrotica]

If you have no welder, you likely don't have a oxy-acetylene cutting torch either.

During the last 50 plus years I've used cutting torches to remove broken off hardened steel, taps, EZ outs, etc. As soon as they get molten you just hit the oxygen, and turn them to slag. You'll get a rain of molten metal, but it works perfectly.

If you get enough experience with a cutting torch, you can remove broken off bolts from cast iron with the torch too. The steel bolt turns to slag with the addition of oxygen, and the cast iron is unaffected. Anyone that has worked in a muffler shop for any length of time will master the art.

That's how I do it, but it requires the correct tools, and some experience to do it.

Rather than use hard EZ outs to remove broken bolts, use the tang of a file where the handle goes on them. You have a square, soft metal, tapered tang that can be hammered into the hole you've drilled. It will grab the inside diameter of the bolt with the squared off edges, and likely turn the bolt out. The tang of a file isn't hardened, and won't shear off like hardened steel does. My father showed me that trick decades ago, it works most of the time if the bolt isn't rust fused to the manifold. Constant tapping with a hammer on the file as you're trying to turn it out helps to free up the threads too. Heat is also the thing that frees up rust fused metals.

If you can't do the manifold broken bolt removal at your house, take the manifold off of the engine, and take it to a muffler shop, they do this stuff daily, and have the tools, and tricks to get the broken bolt out. These guys have the most experience facing these problems every day.

These are my suggestions, having worked on cars as my profession in the rust belt for over 50 years, I hope this helps you get the exhaust back together.