Electric Starter Retrofit

That is the same engine that is in my daughter's pocket bike. Yes, the crank shaft is different than the pull start only engines.
The starter is actually a dynamo. It both starts the engine and doubles as a generator when the engine is running.
Look up Chinese pocket bikes on the web for more info.
No, I have not tried to retrofit the dynamo onto a Tanaka/Mistubishi/Subaru.
I once was interested in fitting one onto my stand up scooter which has the same basic engine but pull start only. The local shop that was in business at the time told me that it would be cheaper and easier to just replace the whole engine and get the proper electronic dynamo controller/ regulator. However, at $250 for the combo I passed on the idea.

It is different but not longer. There is an extension bolt that does the job.

http://www.partsforscooters.com/Shaft_4?sc=32&category=133328

The starter body has the same bolt pattern as the pull start.