Mamoswine: Use the Physical Attacker set here. Stealth Rock in particular would be useful to have, while Stone Edge doesn't help Mamo much (Icicle Crash hits Gyarados anyway). Never-Melt Ice and other type-enhancing items are usually inferior to Life Orb. Life Orb is more flexible and boosts every attack by x1.3. On the other hand, Never-Melt Ice only boosts Ice-types moves by x1.2.
Salamence: Use the Dragon Dance set here. Again, Life Orb is the better item here. Salamence needs the power in order to KO Skarmory and Ferrothorn. Quick Claw is too situational.
Porygon-Z: Isn't viable. If you insist on using it, a Choice Scarf set would probably be the most effective, mainly because the Scarf will patch up its low Speed. Choice Specs could be used, but Exploud does a better job at that thanks to learning Boomburst.
Porygon-Z @ Choice Scarf
Ability: Adaptability
EVs: 4 Def / 252 SpA / 252 Spd
Timid Nature
- Tri Attack
- Dark Pulse
- Ice Beam
- Hidden Power Fighting / Trick
Tri Attack for STAB; Dark Pulse for Ghost-types; Ice Beam for Dragon-types; HP Fighting for Tyranitar, Heatran, etc.; and Trick for crippling an opposing Pokemon, especially a wall. Adaptability for its reliability to boost Tri Attack and help P-Z potentially pull off a late-game sweep.
Arcanine: Use the Offensive set here. Regardless, Arcanine isn't viable. Talonflame, Victini, and Entei all generally perform the physically offensive Fire-type role better.
Heracross: Use the Offensive set here.
Lapras: Isn't viable. Out of the Pokemon you listed, I'd say that Kingdra would be best for your team. It helps weaken Fairy-types and the like so that Salamence can come in and sweep.
Try out either of these sets.