if you rename your messaging app to "UniMessagebin(old).apk" it will still be active and when you paste LGMessage.apk to the priv-app folder the system will use the latest, however you also mention that you didn't replace or rename your .odex file but that is odd since i am thinking it should be
then just copy and paste LGMessage.apk to the same folder set permissions as 644 then reboot? after this it still crashes on startup.
I have a logcat if someone wants to look at it
I experimented with porting the g3 apks together with the odex files, and what ultimately happened was that no changes occured. Then when I tried without the .odex the changes began taking into effect. I was able to port almost all the g3 apps and interface files, except for a handful, by simply knowing where the files should be copied, renaming old files, copying the new files to destination folder, setting permissions then rebooting