Do you still need a condenser with electronic ignition and newer resistor type plugs?
My 73 Chrysler still has the stock AM/FM radio in it and I notice if the engine is revved up a little you can hear a static buzzing noise in the speakers, that you can't hear at idle. Would a condenser help?

back in the "old" days I want to radio shack and asked the counter person for a capistor that went from radio power to ground. the cap passed the buzzing noise to ground. but radio shack is not what it use to be. I would stop down a "tuner" shop and ask for a capistor, may like your old iron to.
joe