Wow this is super weird, I've actually been replacing all the apps in GT's new Samurai rom with the stock ICS apps. So far I have replaced the status bar icons back to stock ICS look, replaced the lg messaging app, replaced the lg phone and contacts, the lg camera and gallery, the lg calendar, deleted the stock browser (why have it when I always use chrome?) and replaced the default system background from the blue gradient to just black. There is still some Optimus interface left but I've pretty much gotten rid of anything LG off this LG phone and everything seems to work just fine
You can try for yourself what I did to my phone,
but I am not to blame if you funk up.
For stock messaging (mms.apk in /system/app folder):
http://forum.xda-developers.com/showthread.php?t=1717648
just go into the /app folder, rename the one already in there to mms.apkbk, drop the one from the link above (a couple replies down) into the folder,and fix the permissions.
pretty much the same process for all the other apps I mentioned, but I'm far too lazy to make a whole tutorial and I have deadlines to meet here at work.
