Nice mods. It is kinda late for my contribution, but flat bar road levers work fine. I am most likely running the ones featured on the moulton above though. It is about time to upgrade SOMETHING on my Brompton.
I have a Alfine 8 with Brompton handlebars, adapted Ergons & gripshift mod if you fell tempeted. You just need to widen the rear triangle a little or I know an LBS that supplies the rear triangle pre-widened to the right OLD.