The problem that I encountered was that the small idler gear was not small enough and would produce tight spots when turning just the cam and the small idler. I have a selection of small idlers and I had to use a used one. When holding both gears and wiggling (one of the gears, not me), it produced very little back lash. After that, it is just a matter of adjusting the large idler to engage both the cam and the half time pinion in the same way, with little play when holding each and wiggling. I found I could use any size half time pinion because the large idler would move in the direction necessary to adjust to it. This cannot be done with the twin because the idler has to be pushed into the two cam wheels, so the half time pinion needs to be selected to fill in the correct distance to the large idler.
David