I'm looking into using an automatic EA81 engine in a wheelchair accessible trike and would like to make the gear section electronic. Currently this will probably be achieved by attaching an actuator to the gear lever. Can anyone think of an easier way of doing this? If not could anyone please tell me the approximate stroke required for the actuator?

You may want to try and use a cable setup. Its not been done here, to my knowledge, so you may look in some other forums. Maybe get a shifter linkage from a AT and see how long the stroke is.