First off, I fully acknowledge that this may not be possible, CORRECTLY... but I have a 1939 house that has been through several generations of electrical wiring. The main panel and a lot of the wiring is from 2010 but there are remnants of every phase of wiring since original.
In a number of cases, I have old AC/BX cable (2 cloth covered conductors with ground as the metal cable jacket) going in to plastic junction, receptacle, or switch boxes. When this happens it is more common than not to have the ground completely unaccounted for, either when connecting to the receptacle or to outbound AC, or even worse, outbound NM/Romex cable where the grounding conductor is just connected to nothing and going to some other location.
What is the best way I can connect a grounding pigtail to the AC/BX cable and make it available to the receptacle/switch/outbound NM/Romex, etc? Is this even possible or do I need to replace the box with an old work metal box where I can install a proper AC grounding bushing and use the grounding lug?