So not knowing how well my plans would work, I decided to keep the investment costs down and purchased a basic Elite manual screen. I wanted to post this for anyone else who is looking to minimize the case height of their projector screen becasue they are in a similar situation: installing a projection screen into a curtain valence.
I ordered an Elite 120" 4:3 M120UWV2 which for me works well as it gives ~96" width, good for my viewing room and it was dirt cheap on Amazon. Originally I was thinking that I would cut off the bracket on top of the case or alternatively take the screen out of the case and build my own mounts out of aluminum angle.
Once recieved, I realized that the end caps are very symmetrical octagons and I could rotate them so that the top bracket is at the front of the screen and thus the overall height was reduced.
To do this:
1. determine which end has the spring drive and which end has a round pin.
2. on the round pin end, remove the screws and end cap
3. on the spring drive end, loosen the screws for the end cap but DO NOT REMOVE the cap
4. while holding the end cap firmly, slide the screen and the end cap TOGETHER out of the case until you can rotate the end cap to your desired position. Ensure the spring drive remains engaged in the endcap
5. rotate cap to desired position. Remember, the elite logo is the front of the case.
6. slide the endcap and screen back into the case again ensuring the spring drive stays engaged in the cap
7. on the round pin end of the screen, tie a short but loose loop of string around the pin and the screen pull down bar. This will allow you to manipulate the position of the pin using the pull down bar.
8. rotate the cap to match the opposite end
9. align the pin with the hole in the endcap via the the pull down bar and loop. Re-install the cap
10. remove string and reinstall the end cap screws. I had to create two new holes but thankfully the screws were self drillers. Ensure one of the screws is on the bottom of the cap.
-I mounted the screen by creating a Z from a strip of heavy stainless sheet metal. One leg was screwed to the top of the valence and the other leg had a hole that matched the hole in the bottom of the cap. Thus the metal supports the screen and the screw holds the screen from sliding off the metal.
-the basic screen material from Elite is quite opaque and does a good job of blocking sunlight.
-the screen material is much less directional than the ancient Dalite Picure King material taht I was using so while on axis the brightness decresed, it was better for anyone else in the room who was more than ~4 feet off axis at my viewing distance (~12').
-by jamming a little bit of wood from a toothpick or a chopstick into the handle, I was able to create enough resistance that the handle can be pushed up out of view and stay there instead of hanging down.