Re: Mercruiser Alpha One 5.7L
*****Without your drive serial number, I say this with reservation*****
It is most likely (again, without the serial number I can't be conclusive), that if the engine and drive are the same year as the boat, it will be an Alpha One.
That said, and heeding the warnings above...
Water pump impeller only 47-89984T4
Repair kit 47-89984Q5 (includes base plate and gaskets)
Lower base kit 46-44292A3
Upper housing kit 46-96148A8
I hope this is what you want, but you MUST verify the serial number of your drive. It needs to be in the range 6854393 to 0D469858....
Please let us know how it goes.
Chris........
(A good idea would be that the next time you're at the boat, record your engine, drive and transom serial numbers. Write them down, and use them here on this site. When you have those numbers, we can be completely confident we are giving you the right advice on service and parts... Without them, we are just guessing. And that can become very expensive, very quickly....)