Hi, im currently building a series 2 with cossie 4x4 engine and running gear. Get youself on ebay and buy a sierra 2.9 XR4X4, the 2.9 uses the same axle seup and the Mt75 box and is more than up to the job, you get LSD's as well slightly different ratio I believe. I have bought 2 now for £100 each....BARGAIN!!!!