I think you might have the pieces that the keyed bushing rides on backwards. The washer goes on the bolt first.
Steve S,
It's hard to tell in a photograph but you may be missing a washer behind the pair of gears.
The sliding gear is kept in position by a thin steel disk that should be between the two gears on the 32T/16T compound gear at the tumbler pivot point. This was a modification of the Stud Gear used on the change gear 10" models.