Saving Old Seagulls

I cannot chuck the magneto and substitute with a distributor, so what about some battery pos power to the points (coil side) with the battery neg to earth. Even as temporary current switched on while pull starting then off when started to continue with its feeble little magneto spark. What voltage would you reckon, 9v ?- I don't want to burn out the expensive Wipac coil unit (1977 Silver Century Plus) Andy