Broken exhaust studs seem to be a predictable problem on older vehicles. Here’s the best way I’ve found to get them out. By the way, it works on most any kind of broken off bolt as long as you have enough sticking out where you can get a grip on it. Also, don’t waste time with vise-grips. Get a good quality set of gripping pliers. You’ll be glad you did.
This clip is embedded here: https://www.sequentrealty.com/rebaranchorbolts.html
The structural engineer calls out the specifc size and spacing of the rebar in the footings and slabs based on lateral, compressive, and seismic calculations. Anchor bolts are embedded within the concrete precisely where sheer walls have been designed to provide the necessary structural bracing.