Thanks for the link to the interesting site!
A brief perusal of a few items on the site (Saint James, the Vespers prayers, etc.) shows me that they are indeed Syrian rite prayers, although in some instances there are abbreviations (e.g., during the diptychs sung during the Liturgy, which are supposed to be much longer than you see on this page), and in other places, borrowings from Byzantine rite usages (e.g., the final blessing of the Anaphora of Saint Basil, which is not how it is done in our churches). I cannot comment on things like the rites of ordination because I am not all that familiar with them.
For legitimate liturgical prayers of the Syrian rite, try:http://sor.cua.edu/Liturgy/Anaphora/index.htmlhttp://sor.cua.edu/Liturgy/SimplePrayer/index.html
I am sure that comparing these prayers to the prayers found on Rik Turner's site (I'm presuming that it is his site) will be helpful to you. In any case, the prayers at SOR are official texts of the Syriac Orthodox Church of Antioch.