I'll edit this with suggestions for everyone.
I hate to start with a perfect, but this guy is perfect.
I would switch his place as lead to Chandelure though, for Bug/Steel leads, Ferrothorn, and because Shadow Tag is generally annoying in a lead. Although I would go with Rock Slide over Stone Edge this time, You have an amazing attack stat and a Choice band to top it off, but if Stone Edge misses you're screwed.
Also looks good, make him your lead.
Consider Fire Blast over Flamethrower, due to PO making Fire Blast and Hydro Pump hit way more than they normally would, and having a bit of an extra punch. And consider something like HP Fighting or Bug for Dark coverage over Psychic. Nothing more to be said
Scald or Hydro Pump would both work better than Surf, Scald gives you the option to not even pull out Willo-Wisp unless you're desprate, and Hydro Pump gives you the extra punch he needs to KO something, Surf still works. ( Also, Hydro Pump like Fire blast hits way more than they should on PO )
I'm a fan of Focus Blast all the way bro, but HP Fighting works a lot better with reliability. Because the reality is, it's not an STAB move at all, if you're using it. It's most likely because you'll be fainted if you don't, and if you miss. You're screwed. Also, consider Thunder over Thunderbolt due to constant rain abuse :]
I think you went the right way with Drain Punch, it gives the same coverage with slightly less power, but it has healing which he really needs, even with Leftovers. Plus, that makes amazing use of the 252 HP ev's you gave him. I would also suggest that you spend some of his Attack Ev's into his Special Defense. Beastly Hp and a 100 base carries you a while, but a few Ev's and you can fool someone into thinking you're actually EV trained in Sp Defense he takes it so well, enough that he can completely recover his damage taken with Drain Punch
He gives the same exact coverage as Regirock, only he has Iron Head.
The set and the Ev's and really everything is amazing for him, but I think you would have a better time getting another pokemon to fill his role, perhaps a physical sweeper. You already have a Tankish Physical attacker with pretty much the same coverage.
But if you want to keep using him, which you obviously do, you'll need to change things up a bit, go for Thunder Punch, Iron Head, Earthquake, Explosion. A Choice banded explosion will put a serious dent in anything that isn't a ghost type. And he has enough diversity from Regirock to play a successful role in your team.
Looks great, no suggestions here.
Except for the fact, that like Regirock, you should take a few of his Sp Atk Ev's and invest them into his Defense, like maybe 64 or so, which with your Hp boost can nearly fool someone into thinking you're completely EV trained in Defense, making them go for a special approach, which is even more hopeless. And I also suggest that instead of that Focus Blast ( Drain punch and HP fighting have that covered well enough ) You should throw in Block instead. This thing is incredibly bulky, and can Paralyze and cripple a pokemon, and then run them through with Blizzard! Which would make for an incredible tank.
I added suggestions, and they're in italics, I hope they do you well, and I wrote a large amount on every pokemon about suggestions for them.