That combo (protrusion and notch) serve to align the crank pulley and cogged gear. There really isn't any holding power there if the bolt is loose (as you experienced). IMHO there isn't any reason to worry about perfect alignment. I would simply install the crank pulley in the correct position as best I could and tighten the bolt to the correct torque. Just make sure the pulley mates up tight against the gear. You can replace the broken piece (gear) when the weather gets better.

How did you hold the crank from turning when you replaced the bolt after changing the belt?? Sounds like it wasn't torqued properly. There is a tool made for holding the crank/pully from turning so that it can be properly torqued. There is also the "rope trick" which you can find by doing a search (or it is probably part of the FAQ's under "Features" at the top of this page. Proceed carefully with the rope trick and pay close attention to the detail of starting from TDC or bent valves can result. Good luck.

Randy