I have an Alpha1. I and trying to get the right lower water pump hsg. I order a sierra (sie-3420) it look like mine but the bottom side where is mount to the lower unit is different. Mine does not have a groove for an o-ring. The one I received has a groove for an o-ring making it about 1/4 longer not letting the base go all the way down. The lower unit was changed out and I have no information.I can’t read the serial # and I don’t know what year it is. The dive shaft is not spring loaded and it has the two bolts above the prop on the bottom. My understanding making it an Alpha 1.