Cheap singlespeed cyclocross conversion

Does anyone have experience with dual gear? I'm thinking about putting a 16t and a 17t cog next to each other. I have horizontal dropouts so it should be possible to ride 34-16 onroad and 34-17 on mtbtracks.
I'm thinking about using a 5/8 speed sram chain.

Just a thought... I've not done it but if you run double rings up front (with no front mech) you don't need to unbolt the rear wheel to change gear, you have a straight chain a all times and bigger difference in ratios.

You could run a 34+36 up front and 18+16 at the back. This would give you;

34x18 = 51 gear inches
36x16 = 61 gear inches

All without moving the wheel or a chain tensioner.