IF there are before current copyright restrictions.

Here is an example -

Selected Works of Plotinus. On the center right, there is a download button - and away you go!

For the "spiritual historian", as it were - either Buddhist, Hindu, Esoteric Christian, etc - I assume that more and more books will become available.  I looked for some Aurobindo in the Free Library, but didn't find it.

The trick for finding the early stuff, is to choose "Full View books" as a search option, and then include free library, as well as what you are searching for. 

Referred by this post from Google Blogoscoped.