I've done this conversion in both ZG23 and ZG26 engines, also with G38. No problem at all, but much better the RCExl ignition than XYZ ignition.
First of all, remove all parts of magnet ignition.
You must drill a hole for the magnet on the prop shaft, insert the magnet well oriented for the sensor , fix the hall sensor, and adjust the timming. On XYZ ignitions, is about 38-40 centered with a magnet of 4 mm diameter.

This is the first start of a ZG 26 , and easy tunning. (this one with a CRRCpro ignition).
http://www.youtube.com/watch?v=LHPfu...e=channel_page
Also i've put a XYZ ignition on Kroma engines , and in JBA glow engines.
See all videos

Regards