Re: "Internal" and "External"
IMO, discussion of :Buddhist vs. Taoist" philosophical, ideological, political and/or religious aspects or meanings of "internal" and "external" takes us away from the bottom-line issue that the OP seemed to be asking, which is, what are the physical qualities of "internal" and "external" body methods that distinguish them from each other.
There are numerous instances where taoist and Buddhist concepts freely intermingle. They are not always black-and-white separate; there is cultural overlap that extends into the martial arts. Taoist and Buddhist thought are utilized as a tool to describe general ideas that can be interpreted on many different levels, both in "internal" and "external" body method arts. For example, Taekwondo talks about Um and Yang (In/Yo, Yin/Yang), but how the concept is manifested and expressed in that (external) art is very, very different than how it is manifested and expressed in (internal) I Liq Chuan.