Finally installed the Sachs Dual Drive 3x7 wheel.

Shimano mtn shifters:


Here's the setup out back. No cable stop, so I drilled the singarm and filed a frame stop flat to bolt it on:


Close up of the cable stop. The wall of the swingarm wasn't thick enough to thread, so there's a nut on the inside:


I also swapped the stock cassette on the Dual Drive out for the stock cassette off the regular 7sp Birdy for more range. There's a bit of slack with the hub shift cable -- the Harris Cyclery website references a cable tensioner potentially available through Bike Friday, but unless the slack becomes an issue I probably won't even bother.

Nice to have the extra range.