Interior surface rust question?
 

I am working on a 69 Nova that is going to be drag raced and street driven. It is a roller that needs floors on either side of the tunnel, mini tubs and a trunk floor. It has no interior so it has surface rust on the inside panels as well. I need an expert opinion on what to do with the inside metal panels once I have ground down the surface rust? Put Por 15 over it (kind of expensive), prime it, use a rust inhibitor like something from Eastwood or Ospho etc. or just leave it and carpet and put the panels back in? What would you do? Also under the car once I have the metal all clean what would you put on there? Do I use the Ospho type stuff and then just prime it and then some chassis paint? Help and opinions please. Thanks a lot.