As you wish:
Pokemon: Arcanine
Held item: Leftovers
EVs: 252 HP, 252 Def, 4 SpAtk (Bold Nature)
Ability: Intimidate
Moves: Morning Sun, Will-o-wisp, Roar, Fire Blast (or Flamethrower)
A great physical wall that burns opponents, making it even easier to wall stuff on the physical spectrum. Has a great synergy with Gastrodon, messes with set uppers with Roar, and can hit decently hard with Fire Blast (yes Fire Blast, not Flare Blitz: this is a defensive Pokemon so the recoil would hinder its walling abilities). If the accuracy of Fire Blast worries you, Flamethrower is also an option.
Pokemon: Gastrodon
Held item: Leftovers
EVs: 252 HP, 252 SpDef, 4 SpAtk (Calm Nature)
Ability: Storm Drain
Moves: Recover, Scald, Earth Power, Ice Beam (or Toxic or Protect)
A fantastic special wall that can also take physical hits from burned opponents and, thanks to its wonderful typing, can force switches and take advantage from the free turns to recover off the damage taken. Scald helps Arcanine spreading burns, which makes Toxic a slightly less useful option for the last slot. Earth Power can deal some serious damage to most Pokemon if you can absorb a Water-type attack thus getting a +1 to SpAtk, and this will make the opponent want to switch some bulky Grass-type into Gastrodon: knowing this, Ice Beam can be useful in the fourth slot to catch them on the switch and deal some nasty damage. Protect helps the passive recovery from Leftovers and makes prediction easier against choiced Pokemon, so yeah, it's your pick in the end...
Pokemon: Armaldo
Held item: Leftovers or Choice Band
EVs: 252 HP, 252 Atk, 4 Def (Adamant Nature)
Ability: Battle Armor
Moves: Rapid Spin, X-Scissor, Stone Edge, Earthquake or Stealth Rock
Armaldo is bulky and hits hard, meaning it can force switches. And you can take advantage of the switches it forces to Rapid Spin. Also, with its powerful X-scissor it can break through Regen cores, which is always nice. If you like to hit hard, give it Earthquake in the fourth slot along with Choice Band. If you prefer durability and support, give it Stealth Rock and Leftovers.
Pokemon: Flygon
Held item: Choice Scarf
EVs: 252 Atk, 252 Spe, 4 HP (Jolly Nature)
Ability: Levitate
Moves: Earthquake, Stone Edge, U-turn, Outrage
Flygon is not supposed to be the hammer of this team. Flygon is supposed to be the scalpel: switch into weakened Pokemon (you have 2 key immunities and many resistances, so it is easy to switch the guy in) and finish them off with the appropriate move. With this set, you can outspeed more or less the entire tier, making this job all that easier. It would be a smart move to default to this guy as your lead, using U-turn to scout the opponent's decisions and get a chance to send in Sceptile and Mega evolve. In general, early on you want to always use U-turn no matter what, forcing switchings and keeping momentum on your side: use other attacks only at the end of the game, when you are sure you can score kills regardless of your opponent's attempts at switching, picking on their weakened mons.
Pokemon: Sceptile
Held item: Sceptilite
EVs: 252 SpAtk, 252 Spe, 4 HP (Mild Nature)
Ability: Overgrow (Lightningrod after Mega evolving)
Moves: Earthquake, Leaf Storm, Dragon Pulse, Hidden Power (Fire or Ice)
This guy hits like a truck. Leaf Storm can deal over 70% damage to anything that doesn't double-resist it (or Blissey), and if the opponent think they are smart, sending out a Fire or Steel Pokemon and then assuming you'll be forced to switch out by the SpAtk drop, EQ will catch them off-guard and score the kill. Dragon Pulse and Hidden Power round off the coverage: pick the type of HP depending on your needs, both can be ok...
Well, this is it. This is a very solid team to be honest, except... I still find Linoone to be the odd name out. This team needs a Volt-switcher like you need air to breathe, to keep momentum going and give Sceptile and Flygon even better chances to come in and wreck havoc...