dCl
I've never seen coning angle directly used even in instrumentation, although it obviously can be derived from the other parameters.
according to our guru, AnFi, it is directly proportional to G load so all you need is a G meter with an additional scale on it
You're right about the Apache but no-one wants to ditch in one because they are a nightmare to get out of and typically roll inverted due to the high C of G.