Your Metagross set definitely seems solid, at least to me!
Personally, I wouldn't recommend replacing Bullet Punch with Hammer Arm. Although latter is much, much strong, former has priority, so it will always strike first (well, at least most of the time). On top of this, Bullet Punch has same-type attack bonus, if I'm not mistaken, which is definitely a good thing. Hammer Arm, however, is more counterproductive, as it reduces your Speed stat after every use.
For Salamence, if it were me, I would likely consider removing Choice Band, and giving either Life Orb or Expert Belt (probably former, as it's the item a majority of players tend to use, generally). Alongside, I'd also give it Dragon Dance (perhaps removing either Crunch, Zen Headbutt, or Strength on the way), as it would make it much more easy to take opponents down after using only once.