When I did my head gasket recently, at first I thought the cam sprocket wasnt going to line back up. If the tensioner has made one more "click" whilst last running, it will have very little slack in it. When pulling the sprocket upwards by hand it can take a fair bit of grip and muscle to pull the sprocket into situ. Of course when you get near you have to start the bolts without letting the tension pull against them and cross threading. Once one is in a good few or more threads you can rock the cam back and forth to help align the other bolt. Tighten evenly feeling for scary tight spots as you go and nurse them in. I have expected to have to release and reset the tensioner (cover off) but I was ok and it runs lovely now (even with water running backwards through the head and running perfect temps, but I digress
)
Tony