When the drapes are closed, you want a straight line of pinch pleasted drapes across the top of the window. So for a 74 inch rod, you want about 74 inches of drape, as measured across the top. What you need to be careful about is how the drapery seller has measured the drape - are they 40 inches wide at the bottom or the top? Check the package and see. If it says "measured overall" that means it is the bottom measurement. A lush, full drape is 3 times the width of the rod, so you need about 225 inches of drape as measured at the bottom (3x74). You are not going to like the look of a string of five or six 40 inch panels on a traverse rod. You could sew them together or just look for something like the JCPenney panels that come in various widths. The cost of triple width panels is one reason many people opt for stationary panels. And it is why you see so many 40 inch panels for sale. Here is a link that might be useful: JCPenney panels

The blog below has some great information on drapery. She has an example of a flat panel with drapery pins placed so that two of them can be inserted into one ring, thus giving the look of a cartridge pleat (that's my description). She calls it a wave heading. I was wondering if you could do this with your rod pocket (I know it won't have buckram in the top, but it should have several layers of fabric) and it might make them look nicer than clips and make them hang better. Here is a link that might be useful: wave heading

I am not a professional but will give you some advice based on my experiences. I made a pinch pleated drape for my large sliding glass door several years ago. We have a wood overhang outside which blocks some of the afternoon sun. I did not line the drape but I did use buckram in the header. The fabric was medium weight home decor cotton...not super thick. After sewing the header, there was a lot of stiffness & thickness in the header for the pleats. If I was to have also included blackout lining in that header, it would have been too heavy & thick for me to work with. It may be a good idea to make a separate blackout lining in your case. I would make the lining about an inch less (than the finished drape) in width as well as length. I have sewn a small window panel that included blackout lining sewn in to it. I did not do pinch pleats for this panel. I used rings & clips instead. The blackout lining was inserted into the header before sewing. I used a double fold of the fabric at the header but did not fold the blackout. The blackout goes all the way up into the top of the header. Same idea for the side hems...the fabric is double folded but the blackout is not. The blackout did not need to be sewn at the bottom...it's not sewn in to the hem. Hope this helps a little. Back side of small drape with blackout (rings & clips) Bottom hem and sides

Two options come to mind: 1. a doublehung with removable sashes. It might be hard to find a company who would be willing to build a DH with such an extreme width/height ratio, however. 2. a true "French casement", where you have two window sashes that open up like a French door.