First of all, "Welcome Aboard", we are a Commander based group here, but the Catalina is a great boat (too) and they share a lot of features, equipment, hardware, and technology with the Commander line. Here is some information that I hope will help.
http://www.network54.com/Forum/424840/message/1181940437
The info we have here suggests you have the Paragon P3 series, in a 1.5:1 gear reduction. I am not aware of any of the Paragons that take a motor oil, all the ones I'm familiar with take ATF.
Hope this info helps you, please double check it, and proceed with caution. Your transmission seems to have another Alpha designation that doesn't appear in the charts we have here so please get another opinion if you can.
Regards, good luck,
Paul