For the taller plugs, Briggs uses this one:
https://www.ebay.com/itm/235873737343
For the shorter plugs it is this one:
https://www.ebay.com/itm/336399683498
Sidebar comment to the OP: I appreciate your interest in "keeping things as original as possible", however.... in the interest of safety I would recommend that you add an additional engine kill button (or better) a kill SWITCH at the handlebars next to the grip for quick/easy access in an emergency.
Michael