Now from what I'm told if you have a kick back brake, tensioners often brake and I know you don't want to weld it on to the frame, I was playing with the idea of a brake arm bolted through the (r) side drop out with 2 small bolts then a 10 t cog (you can get a Pirates), possibly bend the brake arm like we do for the clearence through the drive sprocket, remember when you get your chain get more than enough(double) for what you need.
You can get a so called Sturmey archer brake arm on ebay, I got mine for a $1.o5 chrome no markings,something to think about