Child stoker kits are also different sizes. We have had several over the years (on Comotions, Santanas, Treks, KHS, etc). I would suggest you talk to Mark at Precision Tandems (
www.precisiontandems.com) or Mel at TandemsEast (
www.tandemeast.com). Tell them what you have and they can outfit you with the proper set up, including shims. Your cranks should not hit any derailer, although it may be close.