Into the Mad Doks office for some fixing.

Orks are my second prime competitive army. Currently I'm running Battlewagon heavy, but I see a couple of possibilities for your list already.

The primary thoughts I have are these;

1. You don't have enough Boyz to foot slog.
2. You don't have any good transports.

So...ouch!

Here are my suggestions;

First off, what are those Looted Wagons? There is no official Looted Wagon model, so clearly you kitbashed them out of something. Are they big/small? Could they 'count as' something other than Looted Wagons? (the answer is - yes, they can - it's just a question of what they can count as)

Second off - why'd you list the Stompa? That's an Apoc unit by any stretch...are we allowed to use Apoc units/formations to build your list, or not? Is the Stompa listed because it can 'count as' something else?

Third off - you're kind of heavy on the FA slots, which will be tough to make a larger army with since Orks are silly affordable and you have next to nothing to put in Heavy or Elite slots.

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Once those questions are answered we should have a pretty tight idea of what we can field. My basic advice is something along these lines;

Looted Wagons can count as Battle Wagons

This is easy;
Take 3 Battlewagons.
Load them up with Boyz (I prefer shoota boyz...oh, hey, look, you can do 20 shoota boyz in a wagon!)
Put the KFF Mech in with one of the Mobz.

You now have a very solid core for your army - 60 boyz, AV 14 vehicles, with a 4+ cover save. Truck forward and dump boyz onto any and all threats you can.

Deff Rollas are ace vs. vehicles.

You can supplement the army with deff koptas and bikes.
You can opt to footslog the 30 man shoota mob as ultimate base defense and load the last battlewagon with more choppas or add a Warboss and put in the Nobz and him.

Looted Wagons can count as Trukks

This will be a more fragile force.

Three trukks full of boyz (personally I say 'pfft' to the KFF when it comes to Trukks - why bother?)
Nobz in a Trukk is...okay, but recognize they will have a giant target on their backs (Biker boss will help make target smaller).
Biker boss and Zagstruck are probably the play here for HQs.
If your bikes can 'count as' Nob bikers do it - ignore people who call it cheesy, they are morons who still think we're playing 4th edition/early 5th. Biker Nobz are, at best, okay.
If they can't - just run them as regular bikes and use them as a Dakka platform with the ability to assault (Biker Boss can break off to assault and crack open vehicles)

Deffkopta support is still good for this list.
Big 30 man footslogging mob is also still good, as they can hold multiple near to deployment zone objectives and be tough to kill off as they'll likely always have a cover save.
Zag and his boyz do what they do - they're a very simple unit.

Hope some of that helps.