You don't need the V12 at all because that BMW S70/2 is unobtainable. Try something really different and look for a wrecked E60 M5, E63 M6 Coupe, or E64 m6 Cabriolet.

Then take everything from the M5/M6 for a conversion in to an E53 X5. Make it RWD and call/email Awron GmbH for a custom wiring harness. They make them for any application that someone may want for an S85 V10 conversion. Now that would be an absolutely wicked X5.