banana wall 3" out in middle

[helicopterred]

Hi the building i am referring to is an original extension on the back of a semi built in 1938 with a 2" cavity (the house not the extension) the extension part is built in half brick wall then at some point bricked up inside butted up to the original outer skin making it two separate skins.

I have finally gotten around to removing the dot and dab plasterboard as i have bricked up some windows but now its all bare it is quite apparently bowed due to original doors being bricked up to a central pillar at some point
The wall in the middle is at worst 3" out horizontally

I have a kitchen to fit with wall units so strength is important regarding fixing wall units

Am i best to render the middle to bring it more in line, build it up with Browning plaster or would it be better to stud (i am unsure about the void for mounting units)

Also is 20mm insulation board worth the expense then plaster board on top of that as it was always cold but the rear door was draughty and the roof space poorly insulated so it is difficult to know how bad heat loss is due to the walls?

Any help very much appreciated

 

[chappers]

you could always stud it out then use rail mountings rather than the individual brackets that come with the wall units these could then be fixed through into your studs.