Hey, Kerst. I finally got some time to sit down and play with electronics. The question now is, do you want to set up separate speed controls for each function? Or you could set up one speed control for the carrier and separate speeds for each function of the upper. Can do anything, really. I'd recommend at least each drum has it's own speed control. That way you can walk the hook when booming up, etc.
Each speed control will require a 25K ohm linear taper potentiometer, and a 1000 ohm resistor, and a TIP 120 transistor. You obviousely know how to wire DPDT switches for direction. Adding the speed controls is pretty easy.
I can draw up the schematic for just the speed controllers and let you adapt them, or i can draw it up for the whole complete power pack.
Pot:
http://www.mouser.com/ProductDetail/...tEa96VlWu4c%3d
Transistor:
http://www.mouser.com/ProductDetail/...FOxXz1dSDIw%3d
Resistors
http://www.mouser.com/ProductDetail/...52bdlQPAamo%3d
I found this source online, but I recon you probably have well stocked electronics stores there in NY. The pots will probably be the hardest to find, the transistors and resistors are really common items.