We had this question this week on the Modelsport forum

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Basically, you just need some touring car length shocks (60-64mm length) and springs, and some sort of 'sump' guard made from scrap lexan. And some suitable tyres.

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You can't get massive ride height because of driveshaft angles, but if you don't mind the car looking a bit out of scale, then some touring car tyres (and the body cut to fit them) will help a lot.
Theres a couple of guides online:
http://minirally.cool.ne.jp/http://www.rc-mini.net/joomla/index.php?op...-mini&Itemid=59