The Betrayer +Armored Horse
-Watchers of Karna(12) +Bows(12)

Haradrim Chieftain +Spear
-Haradrim Warriors(12) +Spear(12) +Abrakhan(1)

Haradrim Chieftain +Spear +Bow
-War Mamuk of Harad +Tusk Weapons

Lurtz
-Uruk-Hai Bezerkers(12)

Vrasku
-Uruk-Hai Warriors(4) +Crossbows(4)

Total: 1000pts.

By chance I read your post today, and would like to post my thoughts. It's an interesiting combination of Harad and Isengard. Do you have same idea of a middle earth background story which makes such a mixed army plausible?

Which warrior will be in the mumak's howdah? To be useful, they should be armed with bows. And only warriors of Harad or Umbar or Mahud are allowed, half troll also, but no Uruk-hai.

And her is an idea I got when reading your army list: If you use Mauhur and some marauder uruk-hai scouts, they ca move just as quick as the mumak and could act as guards for it.

(By the way, that's my first post at all in One-Ring!)