Stay with what the 2.4 was equipped with originally. If it was never used, it will still work fine. There is nothing wrong with the mechanical advance ignition that the engine is equipped with. I seriously doubt that you would notice any difference at all between the mechanical and auto advance ignition systems. Neither will provide any more top end power than the other.

To be perfectly honest, I prefer the mechanical advance I have on one of my Brison 3.2s' to the Syncro Spark on the other. It seems to be a little smoother in the transition from idle to power. Don't get your self caught up in chasing the next super widget game. Enjoy it as it is.