Considering this is for HGSS, Alakazam does not have Magic Guard, as that is a hidden ability introduced in Gen V. I feel that between Trick, Thunder Wave, and Flash, Alakazam is just doing too much to cripple a specific Pokemon at a time. If you're dead-set on having him Trick, I'd use a setup like this:
Alakazam@Choice Specs/Scarf/Band
Timid
Synchronize
252 SpA, 252 Spe, 4 HP
-Trick
-Psychic
-Shadow Ball
-Focus Blast
Essentially, Trick and sweep. Those three moves provide basic coverage for Alakazam. Signal Beam is a good alternative move over Focus Blast for hitting Dark-types(because it has better accuracy) as well as other Psychic-types(which leaves Shadow Ball for mopping up Ghost-types). Charge Beam can be used to pick off a weakened opponent and hopefully grab a Special Attack boost. In terms of hold items, I'd honestly go with Choice Specs since it'll greatly boost your offensive power until you Trick it away. Modest is an alternative nature to use if you feel like you want more power over speed.
As for Metagross, I'm quite fond of the Agiligross setup.
Metagross@Life Orb/Lum Berry/Leftovers
Jolly/Adamant
Clear Body
252 Atk, 252 Spe, 4 HP
-Agility
-Meteor Mash
-Earthquake
-Zen Headbutt/Thunderpunch
Lots of different choices going on here. Metagross becomes very threatening after just one Agility, regardless of nature. Meteor Mash is STAB, Earthquake is standard fare, but it comes down to your choice on the last moveslot. Zen Headbutt is great Psychic STAB, and with your newfound speed, that flinch chance is looking mighty pretty. Thunderpunch, however, offers great coverage on things that like to set up, namely Dragons and Gyarados. If you want some extra survivability, you can shift some Speed EVs over to HP, so 40 or 60 HP EVs can help a bit. Item choice is also up to you: Life Orb offers immediate power while Lum Berry can save you from an untimely status. Leftovers is an overall safe option in regards to HP, but may be better suited to a tank or wall, should you choose to have one.