根據畫面的主題內容、構圖和筆墨技法判斷，初步認定創作時間可早到五代，在後晉石敬瑭割讓燕雲十六州之後，即西元936年之後，最晚不遲于遼聖宗耶律隆緒統和初年（西元983年），根據畫面的主題內容、構圖和筆墨技法判斷，初步認定創作時間可早到五代，在後晉石敬瑭割讓燕雲十六州之後，即西元936年之後，最晚不遲于遼聖宗耶律隆緒統和初年（西元983年），即北宋太宗趙炅的太平興國年間。
Based on the painting's subject matter, composition and calligraphic techniques, it was presumed at first to have been made as early as the Five Dynasties, after Shi Jingtan of the late Jin had ceded Sichuan's Sixteen Prefectures, i.e. post 936, and no later than the start of the Liao Shengzong Yelulongxu's Reign (983 BC), namely during Taizong Zhaogui's Xingguo era during the Northern Song Dynasty.

First thing - is all this necessary and helpful? If the client will allow you, then strip it out, because it's not helpful to the English reader.

Other issues:
1. Format - the text carefully distinguishes between two methods for dating the painting - pictorial analysis and text analysis. That seems important, and I think you should keep it. Also, there's no refutation of the dating, so no need to say "at first" "Presumed at first" sounds like you're going to say, "...but actually it turns out to be Southern Song..."
2. The sixteen prefectures are not in Sichuan http://en.wikipedia.org/wiki/Sixteen_Prefectures
3. Taizong's name is Zhao Jiong http://en.wikipedia.org/wiki/Emperor_Taizong_of_Song
4. It's Shi Jingtang http://en.wikipedia.org/wiki/Later_Jin_Dynasty
5. I like the way you've handled the 16 prefectures part, but I think you can do more to make clear how the reasoning works there:
"...the earliest possible date for its production is during the Five Dynasties, after the lost of the 16 Prefectures by Shi Jingtang of the Later Jin, i.e. 936..."

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Note added at 1 day8 hrs (2013-11-18 06:37:50 GMT)
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Oh, and for the last bit: "...during the Xingguo reign era of Emperor Taizong (Zhao Jiong) of the Northern Song."