Easiest way to lower the final drive is to fit bigger wheels.
Other than that its a case of getting an import 5 speed box, bolting it on, getting custom driveshafts, and custom mounts to match it to the subframe.
At any rate 5th gear with a relatively standard F8B would be useless anyway, because the motor doesn't have the torque to pull with low gearing. Now an F8B with forced induction on the other hand...
There's no need to worry about those kind of revs if the engine is well built anyway, Alex. As long as the engine is warmed up properly, running good quality lubricants and serviced regularly you'll get good mileage out of it.
Err, idle? That doesn't have much to do with the size of the wheels champ.
Sure you don't want to know what RPM it does at 100kph? Well the answer to that question is around 4000RPM - the overall size of my rims is the same as most of the guys running 13" rims with 165/65 tyres. The largest overall diameter wheel/tyre combo you can safely have on a lowered MB is around 545mm, which is a bee's dick larger than what I have. Otherwise the tyres just won't physically fit in the rear arches.
