Thanks for all of the replies.
Chuck, I see a mint condition 390 control switch on line, for $25 plus shipping, but from the dark pictures, it is really hard to tell whether it has a middle "neutral" position, or whether it is just forward and backward. If it doesn't, then it would still work, but the neutral position would bring the engine to a complete stop, which would be convenient for any reverse in direction.
Do you know whether it has a center "neutral" position?
Thanks,
Mannyrock