I'm thinking of running three timing belts side by side on one pair of
pulleys. Do you think I can get away with just bumpers on the outside edge
of the pulley and three belts running beside each other? Or will they end up
climbing on top of each other? In other words do I need belt guide bumpers
for each belt? (hard to do in the space available - only room for two belts
then)

..200 pitch by 3/8 wide belt FWIW. I thought I had seen 1" wide belting in
..200 pitch when I started this design. Now, no can find.

Karl