Full knowledge implies they know everything about each other
Manga knowledge means they know only what we are aware they know..
Introductory Argument
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It is without a doubt that Sasori in this Scenario is the underdog character. Not only at first glance does it seem as he has no way of winning , but he's constantly severely underrated due to his loss against the Sakura and Chiyo Combination.
Kakuzu is a skilled fighter, who has lived for many decades and because of that would have alot of experience in fighting all sorts of ninja...Unfortunately, If we were to examine their intelligence, we need not go to the manga to see that Sasori surpasses him in this aspect.. Character Databook 3 has given Kakuzu an point score of 4.5 while Sasori received a full 5. It is clear Sasori is better man in terms of Analytic intelligence...He was able to quickly deduce and determine strengths and weaknesses of opponents and those who stood before him..
When it comes to knowledge of each other, As far as we know they no nothing about each other really.. Sasori himself was stated to be very secritive to people around him... Kabuto , his own spy had never even seen his real face... However, on the other hand, Kakuzu and Hidan are well known as the immortal team.. the akatsuki members would also know of him simply because as Pein said, he has killed every one of his previous partners....Adding this to the fact that pein holds a meeting to tell everyone of fellow akatsuki member deaths and show his respects, he would have become a fairly famous topic... Now , do note I am not insinuating that Sasori knows any of his abilities.
Hiruko -
I really don't believe this puppet would be much of a problem for someone of Kakuzu's level... he has great strength, and similar to Sakura should be able to destroy the contraption by utilizing his Doton Domu technique.. In my opinion once this is out of the way , the real fight would begin as Sasori would bring out the Third kazekage... Note that at this point it is possible Kakuzu still think Sasori is dead, Just as Sakura did..
With the Third kazekage out, Sasori would now take to releasing Producing iron sand by utilizing the third's kekke genkai.. The sand throughout this fight will be paramount in not only proving as a an excellent offence (Considered sunagakures most dangerous weapon) as well as a excellent defense
When it comes to Sasori , the databook makes a few things clear.. One, when it comes to iron sand.. It can become any shape the user wishes, Based on the situation at hand....
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Using this weapon, against an opponent, Creativity is your greatest tool... And in the hands Of Sasori..A genius ninja that takes pride in his creative nature it is even more deadlier than ever..
Kakuzu will come at Sasori with many powerful ninjutsu, unfortunately all will need only defend himself by covering himself in iron sand to render the attacks useless... Similar to how gaara or any kazekage would fight . The databook also shows that Sasori's preferred fighting style is one that puts him out of danger...
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Meaning sand defense and even taking to an aerial state by simply jumping on an iron sand block, would be methods of fighting that he has no problem doing..
With Sasori entering an aerial state, considering they are in an opening field instead of an enclosed cave... Kakuzu would have to then resort to resort to releasing his hearts to attack.... With a mixture of proper defense along with almost undogeable attacks such as Iron Sand showe and iron sand new world.. which use the magnetism kekke genkai to greatly increase their speed
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Sasori would target the things attacking him.. with these very needles.. and as the databook said.. the direction of it even after shot out can be controlled by the magnetism.
We should also not forget, that once a magnetism release jutsu even rubs against the opponent, they are then magnetised and it makes it then impossible to dodge future attacks of the same nature
Simply an introductory argument, not posting everything, your turn