Magpie, I like the idea!

The weight seems to be similar to the VR6 with a turbo, I don't think it's as light as the EJ.

Seems like a very very compact V8 that should most probably fit. There's the question of your axle centers on the gearbox to make sure they aren't too high or too far back of the spindles. If you can make that measurement we would know with enough % of success how well it would fit without frame modifications. You would also know the most probably frame modifications to perform if it doesn't fit well after the measurements.

Of course the RS4 B8 engine would be a killer, especially for the sound!!!! One of the best sounding engine if you do the exhaust right.

You are located in Europe?