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The ONLY concern is whether or not he can snare hard hit groundballs, everything else is elementary. Since he's already played first and apparently done a good job, it should be presumed he will have no problem with this. Furthermore, Ackley is like Ichiro: he's a special talent not because he's bigger or stronger than other players, but because he's quicker and more coordinated than everybody else. As you say, those skills will all but guarantee a smooth transition. If Ichiro were moved to the infield, he'd probably look like he'd been playing there his whole life. We are talking about an extremely gifted athlete. He is much more likely to look like a natural after a month than to struggle and take two or three years to adjust.