I haven't done the research on the actual numbers but I seem to remember that the AMG V8 has a very wide V angle, partly to reduce centre of gravity but also to allow the turbos to be mounted inside the V. This makes the engine considerably wider than the BMW lump - packaging on the BMW engine is tight enough.
On that note, Morgan barely seem to have enough room to plumb a throttle cable let alone, two sets of intake pipework, two sets of pipes to two intercoolers and return pipework to manifold.
It's an epic engine, but the shape would need to change dramatically I imagine.
