Bill, I like the sound of this. I'm working on a 25 Buick right now with a restricted muffler, probably a rat nest judging from the smell of the exhaust. I'm gonna give this a try. The other alternative is to shell out bucks for another muffler which is no fun. I have lots of old diesel around and besides, playing with fire always was something I enjoyed.
And along the line of looking for other causes: It was mentioned above that Kane should check the throttle for full opening. That's a good tip. Bent throttle brackets are common, and can result in incomplete opening as well as a refusal to fully closing to idle.