You have described a conventional Kettering ignition in describing how yours is wired. Obviously the transistor ignition module has failed so someone has reverted to a conventional system where the points switch the coil primary current directly to chassis. In this instance a regular black coil is used.
With the transistor module in use the points switch a much smaller trigger current (to extend their life) from the ignition module. The module in turn switches the positive (rather than chassis) side of the coil primary. In this case a blue coil with a lower primary resistance (= higher current & higher output) is used. If the points are used to directly switch the primary of the blue coil they will have a very short life.
The best option would be to obtain another transistor module and have the system rewired as originally intended. The less costly option requiring greater maintenance (and offering less spark energy) is to replace the blue coil with a regular black one and continue having the points switch the coil directly.
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