As I said before, the heater on my 1976 e12 with factory a/c, still works when the a/c is on, if I want it to. However, while it is still running with the a/c on, the fresh air fan has cut out, but the a/c fan (console blower) is running. Note that early a/c cars had separate controls for the a/c.
So, is it ok to run the heater and a/c simultaneously given the a/c fan (console blower) is still running and blowing cold air behind the dashboard
The reason I would want to run both heater and a/c together, is that in winter I like to use the a/c to stop the seals drying out, and that's more pleasant to do in cold weather with the heater on.