I posted this for the 350 MAG question as well.
In my (limited) experience, I've noticed that the number one thing that will kill an outdrive is a loose nut on the steering wheel.
I've heard that the generally accepted rule is that around 300 horses may be pushing it.
You can pump some horsepower (and torque) through an Alpha 1, just be reasonable on the throttle, and check your bellows regularly. It doesn't hurt to store the drive it in the "down" position.
I'll shut up now.