Take a good simulator and feed it into a REAL Leslie, or motion sound and you'll get that home brewed falavah too ! The rotating horn is more than 50% of the sound, by far. The technique of fast/slow changes is worth at least another 25%, so in the end .... the organ tone itself, is the smallest part of the equation.
I
ve heard DX7s and Casios sound AWESOME through a Leslie 147. It's all about moving the air. Simple physics.