if you dont want to mess about m8,mtx 75 is the only reliable way to goits goin to cost you fair bit more money on the outset,but you will save yourself alot of time money and work in long run.and you will be able to drive the car hard without wondering when the box is goin to self destruct,if its big power id say anything over 200@wheels your goin to destroy bc,ib5 gearboxes easily,been there and done it many many times.
as far as clutches go,depends on what power you want to achieve,but i only use ap or helix.