Oh they're a little different, but your method still works now as well as it ever did. ABC engines only take about 5 minutes to break in, and even a rich first flight will get it done. A proper break in on the ground with the mix set right for it will prevent liner peeling or premature wear though, so it's worthwhile. But IMHO, flying a plane that you haven't set the low end on and verified that it's right just isn't smart. There's no reason to chance a deadstick or engine damage from a lean run when it takes so little time to make sure the needles are set right and the engine is run in right.