Welcome Garry, you’ll find lots of very experienced aeroplane people on this forum.
At the moment you must be one of the few Brits thinking ahead to cold weather!
Our local Aero Club has two Savannas, but both are pulled thru the sky by 912s. This liquid-cooled engine has more scope for fitting a safe cabin heater than an air-cooled Jabiru.
I guess a Jab engine could accomodate a cabin heating cuff around an exhaust pipe, but they’re pretty short and there’s not much room there. It would need to be absolutely gas-tight. You could fit one around the muffler, but it has several leak points; the risk of getting some CO into the cabin is too much for me.
A couple of years ago I installed a cabin heater fed by relocated the oil cooler to the side of the cowling (with an air supply separate from my Jab engine) and set up a flap duct to divert warmed air from that directly into the cockpit. It worked okay, but it could never get enough air to keep the oil cool enough, so I went back to the previous arrangement. My cockpit gets quite a bit of heat from the firewall; in zero-degree air it reads about 6C inside; bearable for a short trip if I wear a couple of wooly layers.
The Savanna cowling probably has more scope for doing something with the oil cooler outlet, as long as you can securely separate it’s air from exhaust gases.