We have a good-sized troop with an elected SPL and three ASPLs who were appointed by the SPL. One ASPL is in charge of our two Quartermasters, our Chaplain Aide, and our OA Troop Rep. Another is in charge of our Scribe, our Librarian, and our Historian. The third is in charge of our six Instructors (Aquatics, First Aid, Camping & Hiking, Knots & Lashings, Map & Compass, Nature Study, and Outdoor Cooking).
I know it is repeated in other sources but it is on page 106 of the Senior Patrol Leader Handbook under "Other Troop Positions" as follows: "With the assistance of the Scoutmaster, you as senior patrol leader will select the Scout who will hold each position." It goes on to list all of the troop-;eve; youth leadership positions.