Here's a pic showing both methods mentioned on this thread...
http://www.travisusd.k12.ca.us/vande...n/DSC00303.JPG
On the top FP Transmission we're using an octogon adapter with a hose clamp that we made back in 2003.
On the bottom Transmisison we've used the plastic coupler that FP sells (used to come in the kit) and acually broached it and stuck a shaft through it. We have also bolted plate sprockets directly onto that plastic coupler.
BTW: That setup was all for prototyping purposes only.