Marc: Looking at your photo, you've got a TD, but I can't tell whether it's got a 2-bow (early) or 3-bow (later) set of "hood sticks" - top frame. The reason I mention that is because the side window frames are different. If you've got the wrong set, things just won't line up well. The early side frames have a 90 degree upper aft corner, the later 3-bow set have radius corners.
Two restoration books have detailed "How-to" descriptions on mounting the side curtains to the frames. Malcolm Green's "MG T Series Restoration Guide" has some information of general use (p. 124,125). The better reference is Horst Schach's "The Complete MG TD Restoration Manual". He has an entire chapter on installing the top and side curtains. Pages 194-196 detail the side curtain steps, and he does mention being careful to position the interior seam so it does not fall inside the framework, as the stitching holes will show when trimming the cloth away. I highly recommend Schrach's book to anyone working on "T"-series cars.