If I understand this correctly, you determined what size 16:9 image you wanted and then came up with a 2.35:1 screen size that could still accommodate that 16:9 image. Is that how you arrived at 160" wide? Why aren't you planning on using any of the extra width for 2.35:1 movies? Your description above makes it sound like you don't plan on going larger that 120" for either format. If that's the case, you could just get a 120" wide 16:9 screen and simplify your masking.