Looking at the mass of the engines involved, I think the VAG V10 diesel weighs in at 258kg/570lb for 300-odd HP. Lycomings are roughly 175kg/400lb for 250HP, 225kg/500lb for 300HP and 250kg/550lb for 350HP.
I notice there is a new BMW 3-litre diesel with 381HP that's c.180kg. If you derated that to 250HP (65% of max), which it develops at 2,300RPM, you'd probably be able to lose at least one of the three turbos and save more weight. At that RPM, it'd be ideal for a direct drive large prop...