If you're going to go with the drop-in K&N, then this thread linked here has an inexpensive mod to the OEM airbox which is a very decent CAI as delivered from the factory. With a simple flow-through muffler like a Mag, Borla, or such, you have a very small investment with the ability to take in more air, flow more air, and more easily get rid of the exhaust...and sound good while you're doing it.
I've done jmr's mod to my '12 Express and have been very pleased with the results with a Borla muffler. No, I have no dyno results, but it's a rare scenario where improving air flow in and exhaust out doesn't help even in just a small way. If this inexpensive intake mod and a better flowing muffler only yielded a 3% increase, you'd still have over 400hp on the Gen4 hemi in our trucks.
The segment of jmr's mod that involves the ram air effect might not be as effective with that OEM fender opening still functioning, as it would bleed off some of the ram air pressure you're trying to accomplish. I'd at least do the additional intake hole with the inlet down low to get the additional cold air effect and increase air flow volume.