Itachi wins this if it's pre-friendly terms Naruto.
I concur, Naruto would be vurenable to genjutsu which would be his downfall and this is speciality of Itachi.
Also even although Naruto know method to dispel genjutsu by stopping chakra flow and overpowering with chakra emission, Itachi would use special type genjutsu known as Tsukuyiomi which would end this.
It is true that Itachi and KCM Naruto were only engaging each other in cqc with maybe one use of Ninjutsu... but we can deduce result based on both Pre Kurama link Kcm Naruto and Itachi performance.
I think it would depend on few things:
1) If Itachi can land Totsuka thrust on Naruto before KCM Naruto moves out of way due to lack of knowledge for example
2) How long Itachi could sustain/keep Susanoo going
3 Could Naruto find out that only chakra arm can grab Yata Mirror and lock it or else Naruto would have no way to harm Itachi.
Because Amaterasu wouldn't work as KCM Naruto would outspeed it.
Anyway I agree.
Post Kurama link KCM Naruto would be win but it would be far from easy win.