The only way to avoid a Revolution is to have some kind of "semi" Revolution, that is, with the heads of the coup informing Isabella that she has two options: to accept their reforms or to settle in Paris. So, with a bit of luck, you can try to have Isabella as a figure head and Serrano and Prim attempting to create some kind of parliament. Narváez would not be a nuissance for too long, as he died in October 1868, and after him, it's just a question of trusting that everything is going to be a bit calmer than IOTL. Of course, you would still have the Carlists, Cuba, the Federalist discontent, etc, but, with a powerless and (hopefully) harmless Isabel II and a peaceful transition towards a parliamentarian monarchy (even if it has to end in the fiasco of the turnismo), you can skip the troubled 1868-1874 period. Of course, if the turnismo begins earlier than IOTL, it's going to show its limitation also a bit earlier...