Converting a standard yz2 to a CA

[Ashlandchris]

My YZ2 is an original standard one. I'm told the 3gear lay down box is better on Astro so I'm going to give it a try. On MB site I can see they do this
https://www.rccarshop.co.uk/spares/y...roturf-15061-p

Do I need anything else? Is the rest of the gubbins already in my current gearbox?
And should I go with a ball diff or gear diff
Do need to change the rear arms for wider ones?

Thanks in advance