| Remember, this is a brass TUNER, not bridge, so alembic isn't going to help.
The biggest problem is not so much the finish, as there are plenty of options available to keep the brass from discoloring.
The problem is more a materials issue- even once you find someone to make the brass worm gears for you (which will cost you $$$$$), they'll wear out really quickly because brass is soft and NOT NOT NOT a good material for gears. Bearings, yes, but not gears. It would cost a lot to make, and you'd end up replacing them soon.
Not to mention the bevel gear, but that would cost less than the worm, but would save the same wear issues.
It would also be pretty heavy, which is not what you want.
Greenman's idea is the closest to reality, but soldering brass to aluminum is difficult enough (search "friction tinning"), but the strength of the joint will be really suspect over time. I doubt it would last very long, as it's meant more for electrical joinery (ie, not under mechanical load). There are welding techniques available, but you aren't going to have the skill necessary I'm guessing. Brass to steel, like if you used older stamped steel tuners, has it's own set of problems.
Themes are all well and good, but this one isn't worth persuing. | 
