If you need brass, do you have the capability to melt your own and mold your own block of brass?  I know there are different qualities of brass, so not sure what quality you need.  You may be able to go to a thrift shop and buy some brass trinkets and melt them down to make your own block...if you have the capability.  I know at the auction I used to work at, brass stuff was selling for super cheap since nobody likes it anymore, but we bought it to sell it for scrap since I could buy it for less than what it's worth in weight.  Just a thought.  I have been thinking about your torque/gearing issue.  If you consider a snowmobile, they actually have a really cool system.  The clutch works on centrifugal force and changes the ratio as speed increases.  Maybe something like that would work for you rather than attempting to add a bunch of pulleys and gears...
