RE: Brisson 5.8 with glow plug
Put a rcexl ignition on it. You can use the original NGK BPMR7A spark plug? or use the smaller BPMR7F tapered seat plug. The ignition caps will be different. for these plugs but the threads and reach are the same. You will have to buy the correct ignition for the spark plug you intend to use
The carb looks to be a Tillotson HL. No reason not to use it?