if you're looking for a plastic kit, i think you can find a lot of them. Tamiya have standard old mini cooper (scale 1/12 & 1/24) n the rally version of old mini cooper (scale 1/24)...
looking at turbo trend, nowdays s/steel intercooler pipping route seems to be it's a must. however looking at stock car manufacturer or some of the US turbokit manufacturer, they seems to be only using normal steel...