Preface to the online edition
These letters were transcribed from the Patrologia Orientalis. Each page of this has the Syriac at the top, and the English at the bottom. There is a list of subjects at the end, but the numbers in this do not appear to correspond to the PO page numbers.There is an extensive academic bibliography of the works of Severus, together with translations and primary and secondary sources at "http://www.cecs.acu.edu.au/severusresearch.htm".