As was already touched upon, you will want to change out the ignition for a more up to date Duraspark system. This will include changing out the dizzy and replacing it with a Motorcraft dizzy, installing a post-'78 ignition control module, coil, and wires.
A great upgrade as you are doing this.....Once you upgrade to a Motorcraft dizzy, source a cap, rotor, and adapter from a Ford 460cid. With this, use the coil that goes with that system, 8mm plug wires, and a plug re-gap. This is commonly called a TFI ignition (Thick Film Integration) and provides loads of spark over the stock Duraspark ignition....
As far as headers, dont bother. The stock cast iron dog-leg manifolds provide ample flow. My 401 pushes a healthy 430 horsepower and I have no issue using the stock manifolds. Upwards of 500hp and I would start thinking headers. The 304, 360, 390, 401 can all use the same exhaust manifolds. The one you want is the one you have.
I
strongly recommend ditching the cast iron intake manifold for an Edelbrock aluminum one. You save a bunch of weight, heat exchange is more efficient, as well as fuel delivery.
I've ran Edelbrock carbs and absolutely love them for crisp response. Where I didnt care for them....in stock form...was anything with a hill.
![Grin :D :D](/community/smilies/biggrin.gif)
The best carb I have ever ran (as far as carbs go) was a Quadrajet. I used it for several years on my 401 before I went full propane and it was a dream...seriously. The small primaries are great for lowend ideling and the huge secondaries will give you the punch you need when you open it up. Offroad, I have never seen a better carb. I could run this thing sideways and straight up and down without a hiccup.
A quick note on Q-jets....a good functioning Qjet is worth its weight in gold. One that needs rebuilt (worn throttle shaft) is nothing more then a flashy doorstop as far as reliability and performance.
I've seen guys build the 304 up to a monster. Cam, high compression pistons, headwork....the 304 is capable of a lot. The drawback is unlike its 401 brother (sister?) the connecting rods, crank, and pistons are cast vs. forged. This is a weak point when looking to increase power. The 304 and 360 also have lower nickel content in the blocks then the 401...this is just an issue of block longevity.