moparnut, I am not 100% sure but I have own a 20Hp autoelectric but it is many years ago and mine had a manuel pullstart cord for "spare".
The autoelectric has another crankshaft then the regular 20Hp with manuel start. It is longer, and this make it possible to mount the dynastarter up on the flywheel.
If the autoelectric has the bracket for pull start then I Think it is possible to mount, BUT I Think you have to leave the dynastart on the flywheel or remove it.
The extension crank will still be there.