Are you jumping off a 6V battery or using a 12V in place of a battery? Definitely use neg to neg and pos to pos if using the 6V battery. I would be reluctant to leave 12V hooked to a 6V battery for long.
If you just want to start and run the engine for a few minutes, I would disconnect the battery cable from the starter and attach the jumper to the terminal and run a hot wire to the coil. This will prevent 12V from getting to your gauges.
Extended use of 12V without a resistor for your coil will result in premature points failure.
By the way, it is better to ask a new question in a new post rather than attach it to another post.
