Be sure the small ground straps (two of 'em) are connected from the rear of the valve cover to the firewall.

Rig some type of ground wires AROUND the hood hinges, both sides.

Be sure the antenna wire is fully seated into the receiver.

If easy to do, try another antenna (yours may have a bad shield).

Resolder the radio suppression relay. You might experiment with shielding around the relay and wires to it, but be sure to ground the shielding material (you can experiment with some aluminum foil).

Be sure the injector grounds are clean and secure at the intake manifold.

Double check the alternator ground wire. Better yet, install another in parallel (can't hurt anything).

Perform the "midnight test."

Snoop around the engine compartment (engine running) using a hand-held AM transistor radio, trying to "sniff out" the source of the interference. Also snoop at the fuel pumps.

Check grounds on the fuel pumps. Try using a capacitor (say, 100 mfd AND 0.05 mfd at 35 volts or more, in parallel -- watch polarity) at the pump or pumps from the power lead to ground.