...and the answer is... It works out of the box! No need for T4 axles, they don't even fit in the steering blocks. I put a pinion two teeth smaller than usual to keep temperatures reasonnable. Weight is more than 1800g.
It handles very decently. Not as sharp as a buggy, but not too bad either. On wet-ish astro I even found it easier and more consistent. Disclaimer : this is my first and only car so I have no point of comparison.
A pic on my X6² :
It looks totally badass doesn't it ?