Everyone’s body is different, but putting on 30 pounds of muscle in that time to look like he’s drawn in the comics is basically impossible.
What is clear though is that Zachary Levi has made significant strides towards achieving a superhero physique and the closer he gets the less movie magic will be required.
Plus, Zachary Levi is a naturally lanky dude, and it’s not as if just wanting to be buff enough will make it happen; it actually takes a lot of work.
Costume controversies arise from time time, but those sorts of things are often disproven in the final film.