5'11" and only 145?? To be honest i'm jealous, you have an ideal body type for the legion. They don't want bodybuilders; all that extra weight just slows you down. You're lighter so can run faster and longer without fatigue and joint pain. Not just that, but without all that extra weight you can probably do twice the pullups and pushups as a lot of the big guys.
If you look at videos of legionnaires, a lot of these guys are relatively thin, and 5'11 isn't too tall at all. If you're athletic like you say, you're going to destroy the other guys in the physical testing part of selection. Now me on the other hand, i'm quite a bit taller and have 60 lbs on you, so I should be worried.