I have used Japanese brake levers before with some success to increase the power of a drum brake. They have a pivot point further from the bar making them generate much more leverage. There are a few of the mid 80's twinshock trailies that still used a front drum brake but I'm currently using a flipped over GPZ500 clutch lever for the front brake on my bullet. It would probably take a degree of modification to fit the twin cables. Span adjustable too.
You also get hydraulic clutch conversions which have a slave cylinder that bolts on in place of the cable termination at the engine end. These effectively pull a standard barrel nipple. I've always wondered if it would be possible to fit one (or in your case, two) of these in place of a drum brake cable and use a hydraulic master cylinder. Venhill stock them.
www.venhill.co.uk/media/downloads/HymecSelection.pdf
Heavy duty brake cable also makes a difference. I had a mate make up a brake cable for my Jawa out of car handbrake cable once and it was awesome compared to standard.
May also be worth contacting your local branch of NABD, this kind of thing is pretty much what they exist for and they will have access to a huge knowledge base for modifying bikes.
The setup for the double hubs and a bullet TLS doesn't look terribly dissimilar. I suppose it's the over locknut distance that's critical. Since you have both hubs, you could measure it. If the spindle is the same diameter and the distance between the nuts is the same, the hub will fit in the forks. Then you just need to see if the anti-torsion lug fits. Remember though, the TLS drums aren't really anything to write home about either so you might just be swapping the frying pan for the fire.