I think that what Simon may be asking is how the kinematics from one translate into the other. If you watch an iaidoka perform jodan, it looks totally different from kendoka doing the same kamae, at least in our ryuha. My wife trains in both kendo & iaido, & we both train in two schools of iai. It was fairly easy for me to understand both ryuha, but when kendo is added in, my wife gets corrected nearly every session for her "kendo hands."
Ken