Sheet Iron will work for the blades, just try to get the blades as balanced as possible.
As for the gearing, I have seen several blowers that have been adapted by using one of the old hand cranked grinders. These are still readily available at most flea market/junk shops. I have seen the fans and case mounted directly to the gear box, and also a pulley could be used to the existing one on your blower. Show us what you come up with.