A Twelfth-Century Tibetan Classic of Mahāmudrā, The Path of Ultimate Profundity: The Great Seal Instructions of Zhang. Journal of the International Association of Buddhist Studies, vol. 15, no. 2 (1992), pp. 243-319.
For a PDF of the original publication via Dropbox, go here.
For an appendix that was never published, a text edition in Tibetan script of ཕྱག་རྒྱ་ཆེན་པོ་ལམ་ཟབ་མཐར་ཐུག་, go here.
The Dropbox links have been dropped, unfortunately, as of July 2014).
Note: I had long ago intended to do a critical text edition employing all published versions as well as several unpublished manuscripts, but time went by and over the years the number of available texts became quite large. The version made available now is the result of comparing only three different versions. Now I believe there are about a dozen, perhaps even more. It may be important to point out for future interpreters that comparing editions of a nearly thousand-year-old Tibetan text is not a luxury but a necessity, as you may see here since no one version has the 'complete' text.