Talking with a flying buddy who has several converted engine powered planes this afternoon and the possibility of fitting the original magneto ignition was explored.
However, just inspecting the flywheel out of the original chainsaw, it does not look like it is straight forward. The flywheel is a combination of a metal hub, plastic surrounding that and a magnetic steel rim on the outside. It might not machine down to a suitable flat flange on which to mount a propellor hub.
Furthermore, it has a printed warning on it about modifying it; could cause it to burst (disintegrate).

edit:
I've just had another look at it and I think it can be done safely by removing a minimal amount of material from the alloy cylinder where the original starter pawls used to engage.