What are you putting it into? If a lower engine would be of use, the 3 liter Subaru with the individual exhaust ports looks like it could be a smooth running starting point.
Peugeot made a pretty slick 3 liter 24 valve - Ford Cosworth Cologne (rare, but slick).
The world is your oyster on this one - if you can't find a 3 liter engine with power potential, you're simply not looking.
BMW M 60 3 liter V8 . . .
Ooooh - that has potential . . .