I have a 1UZ now. Switched after blowing LS7 and LS1 (LS is great, I just needed a change). The 1UZ is just as tight as an LS. DOHC does that. My engine is built, dry sump and has a large single twin-scroll turbo. About 1000hp when turned up. With my setup, water cooled turbo, water cooled wastegates, oil-water heat exchangers, 6-stage dry sump, huge air-air inter-cooler, 2 electric water pumps, 2 radiators - Its WAY busier than a typical setup and can be a PITAman, they are quite long. i didnt even think of that. maybe the lexus v8 (1uzfe) would be a better fit than a RB26 or 2jz i guess.
Part of the problem with a flat plane crank motor is the larger you go, the more difficult it is to deal with vibration. Often in larger flat plane crank engines, balancing shafts are used. As well as active engine mounts. The benefits are many of course. Better exhaust scavenging and less weight in the crankshaft area resulting in the higher rpm's available. Like all things, it's a trade off.Road & Track has just shed some very interesting light on the engine in the Ford Mustang Shelby GT350!
"The Mustang Shelby GT350 is powered by one of the coolest modern engines: A 5.2-liter naturally aspirated V-8 with a flat-plane crank, allowing it to rev past 8000 rpm. Ford estimates maximum horsepower at 526 ponies, but in reality, it's making closer to 600. Not bad for something without forced induction."(emphasis added)