Guess I'll reply to my own post...
I had some extra Acme nuts for the 10TPI rod. So I took a 3/4 particle board and cut a circle, then 2 plexiglass circles a little larger than the wood. Sandwiched between the two nuts it makes a great pulley. I'm actually using standard office rubber bands (size 64) to drive the pulleys and it is working very well.
My desired ratio was 4 to 1, so one pulley was about 4" and the other an inch.
My application is not critical to the millimeter, but rather the centimeter, so this worked out very well.
I now have 2 sets of pulleys working with 2 rubber bands to drive a fairly complex circuit.