Well the rotor doesn't bolt directly to the cam. A locating plate bolts to the cam and then the 3 screws on the rotor screw into it. If you don't have any of the pieces, you're in trouble. That's not a commonly stocked item at the dealer and the aftermarket probably doesn't have such a thing. Also that seal there looks terrible and is leaking. you should replace it before putting it back together. there is also a larger gray dirt/dust/water shield that's supposed to be under the cap also. Did he just toss everything before even looking at what it was?
edit: yes that is the end of the cam you are drilling into if you have any doubts. the plate has a locating tab that fits that slot in the cam so going oversize bolt won't be an issue as long as you do it right. if you mess up you're looking at finding a new cam.
edit: yes that is the end of the cam you are drilling into if you have any doubts. the plate has a locating tab that fits that slot in the cam so going oversize bolt won't be an issue as long as you do it right. if you mess up you're looking at finding a new cam.