Your configuration is "technically" outside the scope of WRC107. The recommended way to evaluate local stresses for an elbow with a stanchion is with the Finite Element method.

For a "quick", "rough" check, you can apply WRC107, but you will have to make a number of assumptions along the way, which could lead to inaccuracies in the results. I apologize for not being more specific, but I can't make these "engineering assumptions" for you.

The Course Notes don't recommend WRC107. What the notes say is "3 - local stresses at the stanchion are only as accurate as WRC107 bulletin". Personally, I don't think the accuracy is there and I suggest you go the FE route.