Thanks for this post. I really want to find a way to syncretize Shamah into the Roman pantheon, because I'm considering taking a priesthood initiate program in Nova Roma, I'm not planning on becoming a priest (atleast, not yet), but I want a solid theological base in the Religio. And I'm most interested in the Divus Augustus, but I've also heard tales of Iulian the Blessed being deified, so I'll have to check that out.
For a theological study, and assuming that people in Nova Roma haven't given you these references yet (they're bound to), I suggest you start with Cicero's
Nature of the Gods and Cato's
On agriculture. It's not that they are a theological authority - Roman religion was and is, after all, one with no orthodoxy - but they are a window to the beliefs held by at least some in Ancient Rome and include parts of rituals, too (namely Cato's work). You might also want to toss in some introductory works: John Scheid's
Introduction to Roman religion, coupled with both volumes of the
Religions of Rome by Mary Bead, John North and Simon Price are an excellent starting point.