Gearing ?

A Gear vender (GVOD) would make my 4.56s worth driving on the street again!
It's a LOT OF MONEY FOR ONE. But simple maintenance and it will out live your 904 many time over. The GVOD will pay for itself many time over.
I do like your 2 speed/3 speed concept:thumbsup:
Just do it, run it, and then build power into the teen as you can afford it. The most fun, affordable time, i have had at at the track was when my car ran low 14s:)