Well, since Shacos damage gets better with AP imo it was a better pick to throw some in to put a kick in your hits so your not brushing your base damage. By the time I have my soulstealer my two-shiv hits roughly 500 damage without useing deceive. I have tried useing a Lichbane in my build and in your build but I never saw a difference that made it worth it. But the problem with a Lichbane in this build is your not souly based on AP, the idea is to be hitting them so fast and LS'ing hp quick enough you cant be beat in a 1v1 fight. In most cases this is true with an exception to tanks or healers in which you use your ultimate.

So if you are focusing on AD/AS, why taking RoA and Soulstealer?
In any possible situation Sheen is still a great tool early game. If you get extremaly fed, you can try going Trinity instead of RoA+Soulstealer.

Also you state that this AD/AS build. I must admit that you have alot of AS but none of your items are accualy AD based.
So you are stuck at your base damage witch is roughy 114 @ lvl 18.
I would squize there a BF weapon or something.

And you have to decide you go AP or AD/AS or hybrid. If hybrid, than TF or Lichbane is crucial.

kinda wierd that you dont get sheen and lichbane later on...