It's pretty easy to interchange it. I had a broken screen and back glass nexus which I transplanted to a new front housing and it was basically plug and play.
From what I saw in the pictures, the Optimus G module is pretty much the same.
I guess that extracting the modules from an 4.3 Optimus Rom and using on a N4 custom rom should do the trick if a skilled rom cooker is involved.
I'm no heisenberg, but could try doing the swap, but as I said, didn't had the cash at the time I saw this thread, and when I got it, due to the lashing, I prefered to go on with the parallel battery mod (which btw is awesome, got almost 6 hours of screen on and 24h device on with very heavy use)