custom GM alt mount

From what I can see, it appears that the OP's bracket (post #22) attaches only at the 2 long bolts thru the water pump. I don't see a 3rd bolt to the head, like the factory brackets and all others shown here. I would expect the alternator mount to be springy in the sideways direction. At a certain rpm, it might start oscillating and perhaps eventually break the bolts from fatigue.