Ok, I forgot to create in the packed exe’s folder the “steam_appid.txt” with the my AppID.
Now overlay loads onto standalone after I copy the dlls + txt file.
Problem solved! Yay! 
For further reference if anyone have trouble with this too:
DLLs must really go into the “\Engine\Binaries\ThirdParty\Steamworks\Steamv129\Win32” even for the packed standalone. Moving to the same exe’s folder won’t work.
The .txt file however must be side by side with the standalone exe.