As everyone is saying, take off Hyper Beam for Dark Pulse if you use a choce item. If you're using any type of other item, throw on Nasty Plot instead. ..I don't know how many times we've said it.
Magnezone only having Sp. atk moves isn't a bad thing, it's a good thing. His attack is terrible, and his only viable physical move is explosion, which doesn't have much merit when you're as slow as Magnezone.
Drop Thunder, Zap Cannon and Lock on all together. Keeping thunderbolt, add Flash Cannon and Explosion or Metal Sound. Not much to put in the last slot but HP Ice since Magnezone's move pool is.. terrible. You could always throw on Thunderwave in the last slot to not only cripple any enemy, but potentially OHKO a faster poke like Azelf. And even if you can't hurt them, you just made them slow as crap and easy to counter(usually). Thunderwave is actually a good move too use if you have no other options(HP Ice).
Just a warning, don't use both Explosion and Metal Sound. I recommend using Thunderbolt, Flash Cannon, Explosion, and Thunderwave personally. T-bolt, Flash Cannon, Metal Sound is a bit of a lesser option IMO, but you can do that too if you want.
Alakazam is a bit tricky, he's a fragile sweeper with a bad movepool, but excellent stats. However, the new trick-specs set available in Platinum is 100% fun and devious.
Alakazam @ Choice Specs
Psychic for STAB, even though it's a terrible move in OU. Focus Blast is needed for good type coverage and to help hit what Psychic doesn't, and Signal Beam is.. not that useful, but it smashes Celebi and TTar with 100% accuracy.
The devious part is Trick, though. You've got a lot of special sweepers on your team, so Trickspecs Alakazam should be very helpful. You know Blissey, right? The ultimate special wall? Alakazam's Focus Blast won't even dent her severely. So, what do you do? Trickspecs her.
If you know a Blissey or another wall you don't like is going to switch in, use Trick. If Blissey is limited to only one move due to specs, it can no longer wall effectively, and just became useless. This is true for a lot of other walls and nearly all physical attackers.
If you trick your specs onto something that doesn't make use the sp. atk boost, you pretty much disabled that poke almost entirely. Then you're free to attack with your other 3 moves. Also, if you get another choice item back when using trick, that means you can trick another pokemon AGAIN. It's a bargain, yeah?