The existing header is made from two 2x 6's doubled up (no 1/2" spacer in between). The wall sheathing that is visible in the photo is 3/4" tongue and groove. The tongue and groove wall sheathing was likely used for the foundation forms and then used for the walls thus the cement stains. The roof is very low pitch--a little more than 1:12. I saw charts that showed 4" (2x4 with 1/2" spacer) as being good for up to 4' spans, but I don't know where the charts came from. Thanks for the response.

I did see the Pass & Seymore combo switch but didn't like the cost and worry about replacing in the future. One of the switches will be used a lot more than the other two. I will probably use three rocker type switches mounted horizontally. One will be a three way circuit so left or right on/off won't matter. The other two I will wire to be on when the left side is pushed in. May look a little strange at first but I don't like the look of separate switches stacked either. The drywall cut would be more difficult too. Thanks to all for the suggestions.