You'll probably not make much headway without suppressor plug wires of some sort.
Here's some things you can do:
Break down and buy suppressor plug wires.
Install the shortest jumper wires you can from the back of the hood to the body--also if you look around there does exist grounding clips for this purpose--they consist of springy brass/ bronze material with "teeth" which you screw to the body, and fit them so the hood bites into them when closed.
Check or replace your radio antenna--they can go bad, you may have a bad ground on the coax feeder.
Get some "feedthrough" capacitors if possible, if not, buy 'any' cap designed for radio noise, at NAPA or (cough gag) Radio
Sh@@ Other caps, like the ones used in old points systems will also work fine. Put one as close to the ign supply positive as you can to ground,with a short lead. (On modern CDI systems, the coil positive is NOT where you want it) Sometimes it helps to also install one on the radio case. The key here is "short leads". The longer the leads--even more than just a VERY few inches--acts as an antenna, so to speak
Sometimes it can ALSO help to add one to the alternator--which should already have one in it, right across the "big stud" to ground.
In older "times" cars with two way --and especially HF (high frequency) radio installations could get very hairy. I remember one whereby the noise was being radiated by the exhaust system--and yep--needed some bonding wires from the exhaust to the body.
Pickups are notorius--cabs and beds not really bonded to the frame Sometimes even the doors are a problem!!
Modern rigs are a PITA---electric fuel pumps, microprocessors, and lots of other noise makers. My old 86 Dodge 600 radiated a signal on the "national calling freq" for the 2 meter amateur band--you could not scan 146.52 MHZ because the car's injection computer would interfere.
