We did the starter by removing the manifold, so we can do that again. I'd like to try from underneath.The knock sensor is a bear to get at. I was only able to change mine from underneath the car. Removing the broken part from the connector will be just as challenging. You'll need long arms, small hands, and plenty of patience for both tasks. As a last resort, removing the manifold will give you much better access.
In another post I see you replaced yours. What tool did you use from underneath? A crescent? Strap wrench? Other?