Clean off the plastic with contact cleaner or brake cleaner to get the silicone and grease off of the plastic. Soap and water will not do it. You might need a razor blade to trim the graphics, depending on how exact they fit.
Put the graphic against the panel before you remove the paper and make sure you know exactly where to start. Start on one edge or corner and slowly press down and remove all air bubbles as you go.
If it is cool where you are, I would take the radiator shrouds and plastic off and do it inside. I would warm (don't overheat) everything with a hair dryer to make the glue stick and also soften the graphic so it will fit the contour of the panel. Oh yeah, after you warm the plastic, clean it one last time with contact cleaner or brake cleaner and be sure the panel is dry before you start putting the graphic on.
Have fun!
JCW