You can get left-handed tapered drill bits specifically for digging out snapped bolts. With a bit of luck, they pull out the bolt without damaging the threads in the block. However, not the end of the world if the threads do get damaged since you can always put a Helicoil insert in to replace the threads. In fact, some engine builders use spiral thread inserts as a matter of course when working since they are much stronger than the threaded iron/aluminium you would normally be tightening into.
With regard to the torque, I believe that torque wrenches are supposed to be calibrated every 18 months (at least that's what my calibration certificate says). They also have to be stored with the right spring tension set, and some are horrifically inaccurate at the 22 lb ft level if their range goes up to ~100 lb ft.