You will need to use a spacer on the crank pulley as the 4.0/4.6 has a longer crank and will not tighten up with the 3.9 timing cover. But it is no big deal. I have ran a 4.6 with the old original timing covers as well as the interim 3.9 ones.Dakar said:We're using an interim 3.9 front cover with the integral post 94 oil pump and distributor hole in the top. It's off a 95 Disco. Bolts right up to the 4.6 block.
We want a 4.6 RRC with considerably more torque than the 3.9, ie. around 300 ftlb. At this stage I'm leaning towards the Turner engine as they have an impeccable reputation for build quality.