cruzomatic,

Depending on the plane and engine, I will break-in my engines in the air. Engines in planes which need power to land I will run-in on the ground.
My first 4-stroke was an O.S. 91 Surpass which I mounted on a Hangar 9 Ultra Stick 60. After completing assembly and initial setup, I brought it out to our club field where I let the club president maiden the plane and fire-up the O.S. for the first time. On the second flip of the prop (done by hand) the O.S. was ready to go. We adjusted the needle valves for a rich setting then I walked the plane to the runway where he promptly took off. He flew it around for a few minutes, putting the plane through its paces right off the bat, then landed uneventfully. The engine ran like a top, and reliably, out of the box with no break-in time whatsoever on the ground.
The choice is yours, but on a plane like a 4*60 with a quality engine I would break it in in the air. Good luck!