Another way of answering the above question:
First, the Simon Necronomicon was written and published without deep research into the archeology of Sumer, Chaldee, and Babylon. Second, it is true that in the late Sumer-ian period, that Marduk had become the primary God of organized worship. It followed that Marduk was then worshiped by many different names.
In the early Sumerian period, Marduk had simply been a deity of war. The next surprise is that the Simon Nec uses some of the most common names for Marduk used in this late period. In other words - the names are at least in touch with archeology. Some of the names are rather poorly transliterated - but they are basically, 'historical.'
In terms of the sigils - my guess would be that they are Simon's own invention. The Sumer's had both petroglyphs and cuneiform script - but I doubt the sigils shown in the Simon Nec have any historical validity. As for the rituals - they were lazily drawn from what would have been massive rites of the organized religion of the late Sumerian period.
Ergo: The Simon Nec does not qualify as, 'historical reconstruction.' It qualifies as, 'contemporary practice.'
I also RP - and I find much inspiration from my gaming and pulp paperback genre fiction reading.
"... And you shall know the truth, and the truth shall set you free..."