Some basics:
High CO is caused by rich air/fuel ratios, but still shows that the fuel is being burned. HC is raw fuel, i.e. the gas sitting in your tank is HC. NOx is how hot the fuel/air mixture is burning. All things equal, the engine with higher compression will have higher NOx readings. If CO gets too low (too lean) then you start misfiring and HC and NOx shoots up. Too rich and your CO shoots up until the point where your plugs start fouling. Fouling means misfire, misfire means unburnt fuel, HC readings go up and since fuel has a cooling effect, NOx goes down. If your NOx and CO are within reason something is preventing all your fuel from igniting.
With that out of the way...
More air won't help if it gets so lean that it causes a lean misfire. Misfires, even inaudible ones, will shoot your HC readings sky-high. 350ppm at idle? That's a tough one especially with no cats. 650ppm is pretty high and sounds like there is a vacuum leak and/or a slight misfire. Removing the air filter element may help but not much unless the filter is really clogged. I'd do a resistance check on the plug wires, clean the rotor/cap contacts (maybe replace altogether) and replace the plugs. If either electrodes on the plugs are rounded off in any way the spark won't be as intense, as sparks like to jump to and from sharp edges. Speaking of plugs, did you check the gap? Try a slightly smaller gap than stock to make it easier for the plug to fire, for example .045 instead of .051.
Try a fuel system cleaner such as the Chevron Techron in a bottle. Also, the chambers, valves, runners, and whatever else is in the intake path might have enough carbon deposits to soak fuel instead of burning it. Give it a few good blasts down the highway in a lower gear (3rd instead of overdrive). Don't give it full-throttle under-load runs as you might soak the carbon with more fuel and raise your HC readings.
Good luck. My 5.0 failed the idle test two years ago but since then it's been in the shop and painted. I'm going to re-smog it and we don't have idle tests anymore. I'm hoping it'll pass this time.