the light is a repro of the old generator lights that were popular in the 60's and 70's. the light mounts to the bars and the generator mounts to the frame seat stay so it can spin off the tire.
it's a good way to ruin your tire on a motored bike. i think there's a post here somewhere where someone measured the voltage coming off one at high speed and it was like 17v or something crazy. that'd probably burn out your light (which is 6v.)
never tried that wiring set-up thing, but the seller's other products scare me.
like this mount: MOUNT FOR MOTORIZED BICYCLE Moped Motor Engine Kit - eBay (item 400166337846 end time Oct-28-10 21:45:41 PDT)
the tank is a hanging tank, designed to mount under a straight top tube. dunno what kinda huffy you have, so i dunno if it'd fit.