As much fun as a Poisoned Life Orb Zangoose would be, I really think Toxic Orb to get the Toxic Boost boost would be better. Though you don't lose any notable 2HKOs with LO. You still 2HKO Amoonguss for example. Other than that I agree on changing Zangoose to a 4 Attack Set and Night Slash over Shadow Claw having used both versions extensively I can say that not wasting time on the set up can let you cause a bit more damage quicker and you don't risk going down to an attack on the set-up.
No Guard Golurk is inferior to Iron Fist Golurk about 80% of the time. After getting rid of Dynamic Punch and Stone Edge you have space for 2 new moves. The role of Fighting move can come from Hammer Arm , Superpower or Drain Punch. Your coverage move could then be Shadow Punch , Return/Frustration or something gimmicky. As it stands with this new set Missy can switch into 2 out of 4 of Golurk's moves so I do recommend Shadow Punch above all others.
252 Atk Life Orb Toxic Boost Zangoose Facade vs 252 HP/252 Def Amoonguss (+Def) : 85.42% - 100.23%
6.25% chance to OHKO