Lets start out simple with the defenses.
81/76/143 stats. I wanted to keep my hp low to increase the gain from maximizing hp and not investing in defenses, because i feel that a 252 hp/252+ atk spread allows us to simultaneously be able to tank the hits from rain pokemon and lati@s, while still being able to apply enough offensive pressure to allow sun teams to grab an advantage. Basically I went with enough bulk to always be able to survive dragon pulse from any boost level of latias, meaning it should ALWAYS be able to check it.
+6 4 SpA Latias Dragon Pulse vs. 252 HP / 0 SpD Cap 5: 309-364 (84.42 - 99.45%) -- guaranteed 2HKO
It also can easily survive one specs latios draco meteor, and can survive 2 scarfed dmeteors, allowing for it to be able to always beat scarf and put specs into a situation where it dies to either sucker punch if it stays in, or pursuit if it switches.
252 SpA Latios Draco Meteor vs. 252 HP / 0 SpD Cap 5: 169-199 (46.17 - 54.37%)
-2 252 SpA Latios Draco Meteor vs. 252 HP / 0 SpD Cap 5: 84-100 (22.95 - 27.32%)
252 SpA Choice Specs Latios Draco Meteor vs. 252 HP / 0 SpD Cap 5: 252-297 (68.85 - 81.14%)
Obviously, Specs latios is a problem, but being able to avoid the 2hko from draco meteor is just not realistic, and we still are in a position where we have a good chance to threaten it, even if you lose a lot of hp in the process. I also kept the special bulk down at a low enough level that an offensive heatran in neutral weather can almost always ohko with fire blast.
252+ SpA Heatran Fire Blast vs. 252 HP / 0 SpD Cap 5: 318-374 (86.88 - 102.18%) -- 87.5% chance to OHKO after Stealth Rock
The Defense stat was chosen to guarantee that Jolly Life Orb breloom will always oho with mach punch after stealth rocks.
252 Atk Life Orb Technician Breloom Mach Punch vs. 252 HP / 0 Def Cap 5: 322-382 (87.97 - 104.37%) -- guaranteed OHKO after Stealth Rock
A low hp stat also has the added bonus of encouraging 252/0 hp spreads, as it means you get a higher percentage boost from the investment.
Now onto the Attacking
stats. Again for attack I worked primarily off of lati@s. 107 attack is essentially the minimum to ohko latios with no hazard damages. This also has the nice effect of always ohko'ing a switching cmlatias with two stealthrock damages with pursuit:
252+ Atk Cap 5 Sucker Punch vs. 4 HP / 0 Def Latios: 302-356 (100 - 117.88%) -- guaranteed OHKO
252+ Atk Cap 5 Pursuit vs. 252 HP / 0 Def Latias: 276-326 (75.82 - 89.56%)
The attack is also enough to nearly always ohko Defensive politoed with power whip, and always ohko specs politoed with leaf blade should it have that:
252+ Atk Cap 5 Leaf Blade vs. 252 HP / 0 Def Politoed: 356-422 (92.7 - 109.89%) -- guaranteed OHKO after Stealth Rock
252+ Atk Cap 5 Power Whip vs. 252 HP / 252+ Def Politoed: 326-386 (84.89 - 100.52%) -- 87.5% chance to OHKO after Stealth Rock
The Special attack is mainly filler, keeping it low enough that Scizor won't be ohko'd by hidden power fire, and it also allows me to get a nice round number for my bst (525), which is always nice for optics.
The speed is 76 to make it as hard as possible for specs politoed to speedcreep you, while still keeping cap 5 slower than hearten.