I would be tempted to keep the coil feed from starter solenoid to your new non-ballast coil in-situ and, as TBM suggests, remove the ballast resistor and connect its feed direct to new coil. See GoMog diagram below to illustrate.

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The effect will be to place two parallel electrical paths to coil whist starter is energised. The improvement will be miniscule in reducing volt drop but may just help with slightly better spark under adverse conditions (poor battery, cold weather).

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone