PulpFriction

Don't do that yet. And I'm pretty sure you're talking about the VVT solenoid valves, which sense nothing. Pic at comment 53 above. The cam position sensors are on front and back of the head on the driver side. But none of those are like to be related to a single cylinder misfire.

What exact plugs and coils did you use in replacement? The p/n's.

Did you happen to do a compression check when the plugs were out?

How many miles on the car? Any prior or other history of engine problems?

Strongly recommend you get hooked up to a capable scan tool, one that will read all codes, not just P codes, and post the numbers here. All of them, even if you think they're unrelated.

donbrew

Is P0304 the only code? Anything you assume is not relevant.
Have you done a compression and leakdown test?

RJ_RS_SS_350

If it's not a plug or a coil, the other possible culprits are an injector or gunk in the fuel rail, or a mechanical problem (diagnosed with the compression or leak down test that donbrew mentioned.

HB2

Those are the numbers on the scanner while engine is running.

HB2

No other codes and no compression test or fuel rail cleaning, yet.