Well, the plugs are the source (with the spark generating a wideband RF noise) and the wires and coil and all are the radiators.
Ford's DIS in the Ranger is TERRIBLE that way. There are a few solutions.
1. Many years ago, hams did take the braid off some RG/8 coas, and smooth it over the spark plug wires, grounding it at one end or both (depending on what worked best, lol).
2. I have snap on ferrite chokes on all 6 spark plug wires. This cut it about 50%, but did not eliminate it. There are different types of ferrite material that is better for some frequency bands and it's possible a different snap on toroid would have been better -- but the ones I got I bought surplus from http://www.allelectronics.com
and you never know quite what you're getting.
3. Have a better radio. Good ham and CB radio's have noise blanker circuits that work. Both my Maxon CB and my Kenwood ham rig have them and it's like NIGHT and DAY. Get a radio with a noise blanker or "ANL" circuit (different names for the same thing).
If it's definitely ignition noise, that's probably it. Ford is famous for fuel pump noise as well -- it's a more constant buzz that is somewhat affected by motor speed, but not much.
The reason it's so bad is the same reason Ranger's don't benefit from aftermarket ignitions -- the DIS is really "hot". The resistor in the plug (or the "resistor wires") that is supposed to help limit the di/dt when the plug fires is a bit small for the voltage of the ignition coil. So when the plug fires there is a sharper rise time, creating much more noise.
Also, make sure you have your radio's grounded well. It's part of the reason I am so fanatical about NOT using "body" ground but instead running an 8 ga wire back to the battery. There are too many circulating ground currents and noise in a modern electronic automobile for that to work well -- especially at higher frequencies.