I like your thinking on this, @davidjblazo, and I really appreciate how you are attempting to show that even a materialist conception of morality may prove to be an apologetic for the existence of God.
My first thought in reading your proposal was its similarity to Sam Harris’ work in The Moral Landscape in which he attempts to argue that moral reasoning can be reduced to states of well-being, and assigning value judgements on the basis of these cognitive states. I think there is a great deal of similarity between his conception of a materialistic moral theory and the thesis that you have proposed, albeit with the very obvious distinction that you believe that this would point to God while Harris does his work in order to rule out the necessity of positing anything non-material.
Another thought that I want to address is how you framed the whole proposal. You set out the following propositions:
God is the author of the natural world
God is also the author of morality.
Therefore, science (that is study of natural world) can also ascertain morality.
I think that the conclusion of item 3 is problematic because it doesn’t necessarily follow that because God is the creator of both morality and of the natural world that these are overlapping domains of which science can investigate.
Let me use an analogy: CS Lewis wrote both The Lion, the Witch, and the Wardrobe in the Chronicles of Narnia series, and Out of the Silent Planet from his Space Trilogy. Let’s suppose that I’m a studious investigator of all things related to Out of the Silent Planet, and then you ask me the question, "who is the first person to step into Narnia in The Lion, the Witch, and the Wardrobe? Simply because CS Lewis wrote both books, it doesn’t necessarily follow that a question about one will be able to be answered by the other. Sorry for the silly example, but similarly, it isn’t necessarily the case that simply because God created both the natural world and morality that we are able to find the answer to a question about one domain of the other.
Now, we have to be careful, because it could be the case that we can ground our morality in the natural world, but it does need to be the case. Because of this, I think your first argument would need to be why we, as Christians, should attempt to ground our morality in the natural world.
Going back to Harris’ book, he must to ground morality in materialism because he has already committed to materialism, or else he is left in moral relativism, as many non-theists have concluded and as Harris really doesn’t want to conclude. Moreover, he is left with a functionally utilitarian system. Though utilitarianism is very intuitive for many people, there are some substantial difficulties that it needs to overcome (happy to elaborate more on this). In contrast, I think there are some substantially more robust conceptions of morality for the Christian that need not be utilitarian nor rest on the premises of the materialist.