Brenton's. But your question is very much on target. Of the three major versions, the most recent one (5th century) Alexandrian agrees with the KJV (Hebrew) more than the previous ones (Vaticanus and Sinaiticus, 4th century versions). The Alexandrian is known to be the least reliable, and most altered. But then so are all the other Bibles to various degrees.
As for the verses mentioned, they are significantly different, even though everyone seems to be in denial. One calls the son a messenger (aggelos) of the great counsel – i.e. of advice, opinion, etc.
The other one calls the son mighty God, The everlasting Father, The Prince of Peace!
I think it takes an active effort of self-delusion to "see" both of these verses as saying the same thing. I submit that someone familiar only with the LXX versions would get a very different impression who the son is from someone reaidng the KJV version.
In the former (LXX), which was the Christian OT, there is no divinity even implied. In the latter (KJV), which is ironically the Hebrew version, the son is called Mighty God, even the everlasting Father, the Prince of Peace.
Likewise, the implications of the verse 9.8 are opposite unless, of course, the reader chooses to bury his head in the sand. In the LXX version God sent death upon Jacob and Israel, and in the KJV version God sent a word (knowledge) into Jacob and it (the word) (en)lighte(ne)d Israel.
Contextually, the chapters may be the same overall but that is a stretch considering how different impressions and meanings are implied in its various verses. You can, of course, believe whatever you like. But I have yet to hear a plausible explanation how can death and word be one and the same, how can death and enlightenment be one and the same, how can a messenger of great opinion be the same as Mighty God, everlasting Father, how can "I will bring peace upon pounces" be the same as the "Prince of Peace."
οτι παιδιον εγεννηθη ημιν υιος και εδοθη ημιν ου η αρχη εγενηθη επι του ωμου αυτου και καλειται το ονομα αυτου μεγαλης βουλης αγγελος εγω γαρ αξω ειρηνην επι τους αρχοντας ειρηνην και υγιειαν αυτω
and
θανατον απεστειλεν κυριος επι ιακωβ και ηλθεν επι ισραηλ
Is the numbering different in English too? By the way, that KJV translation isn't even close to the LXX Greek. You're right.