Also check the ends of jackshaft where snap rings are. These are known to wear.
The Heald bike is similar to the Heathkit Hilltopper (both companies were in same building and Heath used a lot of Heald's ideas in their Hilltopper kit) same or very similar TC setup, jackshaft with band brake, fenders, etc, etc.
Not sure if anyone mentioned the kill switch question, there is only one wire because when you push kill sw button it makes contact with handlebars which is the ground and "killing" engine.
The single wire from button usually goes to the middle pin of 3 pin connector coming out side of engine.