Rule of thumb
Use the "J" distance which is the distance between the headstay and the front of the mast. In the case of a 272 that distance is 10'-6". I use an adjustable whisker pole. It stabilizes the jenny when I sail downwind. You can adjust the pole from that baseline dimension depending on the wind speed. You should rig a downhaul from the pole end. It helps keep the shape of the jenny and prevents pumping of the sail. I use nylon line and lead it back to the cockpit from a snatch block mounted at the base of the stanchion post.This is not a sophisticated rig, but as someone else has pointed out, a spinnaker pole is used to fly a spinnaker and requires much more tending than a downwind setup for a jenny.If you need rig dimensions for your 272, try pyacht.com.Tom