The whole engine should be considered as posted.
That change to an electric starter includes, replacing the early alum cover with a cast iron starter hog's head (trans cover), later low pedal with offset to clear the Bendix cover, the starter and Bendix, a later flywheel with ring gear mounting groove, and ring gear, and the location and provision for a high amp 6v storage battery and related wiring, and if desired, some sort of alternator or generator to recharge the battery.
Replacing with a later ring gear flywheel means the transmission and magneto is disassembled, reinstall and/or re-charge the magnets, then fit the triple gears to the new flywheel posts, that may or may not mean to replace gears or pinion posts in the flywheel for proper transmission operation. replacing the coil ring may be good too at that time, and measure other points like rear main bearing to be sure all thrust tolerances are OK.
It's not all that difficult, just a lot of things need to be considered and adapted, and planned for.
Picture of non-starter trans, with plain flywheel, the other is a later ring gear flywheel, and difference in early and starter type low pedal connection.