Looking good, especially if you can lure their stack into the firing line of your cats. Shame about the spear and axe - I think you need to get yourself a sentry chariot. 
I think I'd push on to Alcatraz and make Avio choose to defend there or attack Nobamba (if you leave a small enough garrison in there to make it tempting, you can leave some reinforcements 1NE of the city to take it back again if he does attack - also he won't be allowed to burn it, so you don't lose the city, although you might lose some buildings.) While your stack is so much bigger than his you should take advantage and you can afford to lose all your units as long as you kill him in the process (losing them without wiping him out isn't so good though). Once he has construction things will change quickly.
I don't think the border pop in Nobamba will help you by the way - there is too much Zulu culture in the way.
I think I'd push on to Alcatraz and make Avio choose to defend there or attack Nobamba (if you leave a small enough garrison in there to make it tempting, you can leave some reinforcements 1NE of the city to take it back again if he does attack - also he won't be allowed to burn it, so you don't lose the city, although you might lose some buildings.) While your stack is so much bigger than his you should take advantage and you can afford to lose all your units as long as you kill him in the process (losing them without wiping him out isn't so good though). Once he has construction things will change quickly.
I don't think the border pop in Nobamba will help you by the way - there is too much Zulu culture in the way.
Completed: RB Demogame - Gillette, PBEM46, Pitboss 13, Pitboss 18, Pitboss 30, Pitboss 31, Pitboss 38, Pitboss 42, Pitboss 46, Pitboss 52 (Pindicator's game), Pitboss 57
In progress: Rimworld
In progress: Rimworld