There's a bit much to follow there flywheel and when it comes to electrics I'm no expert - but - for definite you want a big chunky cable (e.g. battery lead) from one of the starter mounting bolts to an earth on the chassis frame (acceptable) or directly back to the battery (preferred).
By the way, when you say you bought a 6V battery, what kind of 6V battery did you buy? A proper one should crank the engine for quite a while in new condition and fully charged...
By the way, when you say you bought a 6V battery, what kind of 6V battery did you buy? A proper one should crank the engine for quite a while in new condition and fully charged...