can we say ”我很长时间看书“？meaning I have read a book for a long time. is it possible to put duration in the beginning?
“我很长时间看书” is grammatically incorrect, because any time expressing duration, in Chinese, must be put behind verb + object.
However "我看了很长时间书" will be correct, though, since 很长时间 here MEANS a length of time, but ACTS as a noun. Actually, "的" is hidden in the sentence, so the non-abbreviated version will be "我看了很长时间的书".
"我看书看了很长时间" is conveying the same meaning, but since the verb is used twice, one tries to emphasize on the action being done by using this.
Yet after all, the most usual one being used by native speakers, I think, will be "我看了书很长时间"
"看书“ is detachable word， that means we need to put temporal words(such as 很长时间）into the middle of "看书”。Detachable word can be collocated with many kinds of word or phrase and the collocation with quantitative phrase is one of the most common occurrences。 So the correct answer is "我看了很长时间书" or "我看书看了很长时间”。
If you still don't understand this grammar point, I recommond you to buy one or two good Chinese grammar book, this articel tells you the best Chinese grammar book.http://www.hanbridgemandarin.com/article/chinese-learning-tips/best-chinese-grammar-book/