Take 10 boxes of Airfix 8th Army.
Take 4 boxes of HaT British Heavy Weapons.
Take 2 boxes of Strelets New Zealand.
Remove the heads from one box of New Zealand troops and put those heads on randomly selected Airfix and HaT figures. Put the Airfix and HaT heads on the headless Strelets New Zealand guys.
Co-mingle the various guys together and you have a New Zealand battalion for the Desert with the vast majority wearing the standard uniform with helmet and yet just enough with the lemon squeezer to give the impression of a unique New Zealand force.
Head swaps are quick and easy, I do them all the time and I am not much of a conversion guy. I have explained it a couple times on my blog and will explain it here if anyone is interested.
As for painting, I usually just paint figures an overall color so the unit matches.
Mike kinda beat me to it but headswapping seems the answer - perhaps Strelets might like to consider building that into their sets and supplying a set of alternative helmetted heads, so that people don't have a to butcher a whole set of unfortunate figures. Call me squeamish but I always hate cutting the heads off figures, it's as though the headless figures have been denied their destiny! (I know,I know they are only bits of plastic, but being sane was never a particular requirement of this hobby).