Hi Mike - I think Rick and I were attempting to address your question. The mind set is an important component of "internal" arts. As mind set is an important component of "external" styles also, I would invite you to entertain the possibility that the distinction is artificial. Henning makes a damn good case for that possibility using copious historical reference material.
Nagamine Sensei of Shorin-Ryu stated at a banquet that when he began his study of the arts he considered his path very distinct from others. As he approached the higher elevations of the mountain, he saw that the various paths tended to converge.
I would submit that advanced practitioners of almost any martial art will tend to embrace similar concepts, movements, and strategies. Some start out "hard" and become "softer" and some start out "soft" and hopefully become "harder" (if they are attracted to the martial aspect of the "internal arts" and if they have a knowledgeable sifu.
Ultimately the synthesis of mind ("yi"), muscular power ("li") and intrinsic energy ("qi") must be present for any martial artist or champion athlete. I think of qi as the neurological raw material from which conditioned response patterns are forged in the furnace of repetitive focused training.
I've heard it said that to know the house of Chen one must quake. This refers to the uncontrolled shaking of the extremities as one stands in low postures for long periods of time in an "internal" style. In a traditional Hung Gar school guess what the first order of business is for the first year or so...you got it - stand in low ma bu (horse stance.) You tell me, what's internal and what's external?
I think (from what I've seen - not the last word in anything) that if you took an advanced practitioner of one of the Taoist internal traditions, a Wing Chun fighter, a Uechika, a practitioner of Silat, etc, etc. and placed them in real combative situations not sport application, no visible denotation of their style - you would have a hard time telling who trained what.
You would be able to identify specific strategic choices based upon their perceptions of their opponent, i.e., bigger, smaller, stronger, weaker, fiercer, more frightened, slower, faster, good with kicks, no kicks, etc, etc, however, the "stuff" won't look that different. What is always different however, is the mind set. It is the "36th Chamber" where the real issues are settled. To that extent, I will always visit Canna Sensei's forum as he is a strong spokesperson for that reality.
I have a Wing Chun brother who really doesn't train very much and is overweight. He has decided that he will ALWAYS go home to his wife and kids though - NOTHING will ever stand in the way of that. This captures my attention and diminishes the relative importance of a debate over what is internal and what is external.
I think you would really enjoy Frantzis' book that Rick mentioned. He is very biased but gives a down to earth rap on the subject.