With the correct (or close to it) timing, idle should be much lower and smoother than with glow plugs. A glow fueled engine might tolerate more ignition lead time than the same engine on gasoline, so you might have to experiment to get the best high speed timing. One good side effect of all this is that carb tuning will no longer influence ignition timing as with a glow ignition. You will be able to achive the best mixture setting without playing with glow plugs and altering compression shims.