Q-4's had both road pilots and switching pilots although all 135 were built with road pilots as I recall. I do not believe that the use of the auxiliary tenders depended upon which regular tender was used.
I see that you are a member of the BSME. Perhaps you can have Doug A. introduce you at some point. I live above Baltimore and know Doug well. I have some knowledge of the B&O from steam days as I saw a lot of Q-4's running.
Interesting. I intend to use my 4625 as a short line locomotive, so maybe the switching pilot is more appropriate. I talked with Doug for a bit about this during a meet. Apparently in the book Q (Which I need to get a copy of) it talks about the 6 water bottles the B&O had. Allegedly the modeled tender is 2 S1 tender water tanks soldered together. It was specifically made to be paired with the tender Westside modeled.