I will now elaborate. The abbreviation used for 'Utnapishtim' is 'Na'ish', the pronunciation that would have been used in Palestine around that time is 'Noah'. This is one suggestion that the biblical version may be plagiarise. Have a read of The Epic of Gilgamesh and Atrahasis. Both contain the same story. The reason I suggest to have a read of it is because the narratives are eerily similar.
As for dates, Ziusudra and Gilgamesh are recorded in the Sumerian list of Kings,
Interesting you'd pick up on the proportions of the ship. Could the ark actually carry all the enough of every animal in the world?
The food they need to survive for 40 days? And the compartments to store all their poop?
So much for the measurements of an ark being realistic. Unless of course Noah only needed enough species for evolution to occur, but sadly, science the evolution of existing specifies were not that quick.
Interesting (I looked up to see where you might have got your information) that the proportions in Atrahasis aren't mentioned, I can't remember them off of the top of my head so I'll have to dig out my copy later and see how they compare. (And also check Gilgamesh to check the accuracy as the sources seem to be from Creationist websites and generally I find they like distort the truth)
On the note of the realism of it raining 40 days and 40 nights. No, it's not realistic. But of course, it's divine intervention. But if it's divine intervention then why would the number of days matter? Surely a god would have the power to flood the world in 7 days? It'd only have to rain 5.71 times as hard. Maybe this suggests the Mesopotamian gods are simply more powerful?
Another striking difference between Genesis and the other versions is that in these accounts the hero is granted immortality and exalted. The Bible moves on to Noah’s sin. Only a version that seeks to tell the truth would include this realistic admission.
But Noah lives for an unrealistic number of years. Hardly a realistic admission.
Speaking of realism
The almighty all knowing God finds that his creations are too evil and decides to wipe them out, but picks a select group of humans he deemed worthy to repopulate once the flood is over. But these humans are just sinful as ever. God did not foresee that this would happen and once again he's got a population of sinful humans again. So much for 'fixing' things. Hardly realistic for an omniscient and omnipotent being.
The Mesopotamian Gods on the other hand, a little more realistic, they actually have their own flaws, they don't try and claim perfection. There were a group of gods who agreed to flood the world and wipe out the species, but one god disagreed and sought to give everybody a second chance and he contacted Utnapishtim/Atrahasis/Noah to save all living things by building an ark.
But in real realism, it's all unrealistic.
Plus this version of the story is much older than the accounts of the bible. Where would have the Jews got the more realistic account? Surely they got their version from an earlier version of the story? Storytelling has a habit of changing a story as it gets past down each generation.
But I will leave with a final note. The Canaanite religion, it's got interesting connections to Abrahamic religion and Mesopotamian. Kothar-wa-hasis (a Canaanite god) shares the same epithet as Atrahasis and Kothar-wa-hasis is the god of craftsmanship. It'd make a fair evolution in the story of a craftsman who'd become immortal. Yahweh is another one of their gods. I don't need to say who Yahweh is.