Rod BOPs and stuffing boxes are both outside the scope of API 6A. Applying the API 6A monogram to either of them would be a violation of the monogram license agreement.
Stuffing boxes are outside the scope of API 16A. Applying the API 16A monogram to them would be a violation of the monogram license agreement.
Also note that API 16A is for Drill-through Equipment, so a drilling BOP can be monogrammed to API 16A, but a production BOP is not allowed be monogrammed to API 16A.