[Alex V.]

If it starts and idles remotely right on all 6, don't judge anything about your engine's state of tune until you can drive it. And you aren't doing it any favors by just idling it repeatedly like that. It likely won't hurt the old 6 but it won't help it any, either - maybe once every few months, but even at that rate run it until the thermostat opens. Once you get it road worthy change the oil, take it out for a jaunt with some highway running, then pay some attention to your plugs.