When I built up our Comotion Speedster (size Small), I was surprised that I needed more than one chain's length to meet the length requirement for the timing chain only. Seemed like almost two chains worth, but not sure - it was long ago. Different bikes will have different lengths of timing chain, but I remember being disappointed from the extra weight that I did not account for. Thinking of riding the tandem again, and trying to lighten up, so Gates drive might do it for me.

This thread might be dead by now, but it is something to consider.