Took a old 3/4" drill bit and shaved the sides of the flutes down gently with a fine sanding disk, couple of passed at a time on each side till I got the correct width. Used a 5/8 bore pulley as a donor. Quicker than a drive into town to buy a pulley and worked great.
As for slowing the machine down, old story. When I was a kid, went with my father to help him do a esitmate for a sprinkler system in a sewing factory making jeans, etc. They had a bank of machines running at a slower speed just for the new employees, till they got the hang of using the machines. The regular machines would do a side seam in a couple of seconds.