I have only limited knowledge, and I've forgotten half of what I once knew, but here are a couple of items:
1. The radio needs to be tuned to your antenna... I've forgotten exactly how it's done on your radio, but usually there's a hole in the faceplate (may be behind one of the dial bezels) into which you slip a long skinny screwdriver and adjust it to get best reception to a very weak AM station nearest a certain frequency on the dial (unfortunately, I also can't remember which frequency, 800 comes to mind, but a search on Google might get some info, or you can ask your radio repair shop).
2. Do you have the distributor and spark plug/wire shielding in place?
3. You could try disconnecting your alternator for a short test run to see if it is the major source of your interference.
4. The antenna passes through (and is fastened to) the center of an antenna "plane"; it is a sheet aluminum plate just below the surface of the rear rear deck, about 6 x 12 inches in size. That plane, in turn, is connected to a frame ground via a ground cable. Check to see if the plane is there and your connections look OK (may not be easy to see).
In my experience, the static collectors are not a major item in reducing radio interference, although they probably have some effect or the General wouldn't have put them there; most of them disappeared the first time a Corvette owner removed the caps.
I don't know how to test capacitors.
