You would need a looong bottom bracket axle if you used the Middleburn Uno (same applies to White Ind Eno) - it has the wrong chainline for a Rohloff (54.5 iirc), which if you look has the sprocket much further out on the axle compared to middle cassette positon of a ss. I've looked into this, a standard crank and use just the middle ring. I think a modern Middleburn square taper with a four bolt xc spider, and a Thorn reversable 38 chainring would/will be my ultimate choice.
You won't need bigger than a 38 off road, especially with a big wheeler..
Happy hunting!