I could see how more compression would make it idle smoother; a more powerful power stroke would tend to do that, especially given the stock 6:1 compression. What always amazes me about those engines was how long they would last, and how hard you could work them...with NO pressurized oiling system. I've seen them idle down to about 3-400 rpm and still run smoothly.
Has Ollie been working on that C cab?