Not a BassBoat Guy but I'd imagine you'd want to get the same GPH that's in there now. From what I hear on this Forum and elsewhere the ShurFlo brand is as good as any!!!
Not sure what type pump you may have or talking about. Is it a circulation/aerating type pump or thorough the hull type? If it is used to fill the live well, It is probably a through the transom type pump. So look at the lower transom for it. JMHO!