The Viper engine has an odd sound no matter how its exhaust is set up. Not necessarily bad, but I like a 600HP mover to sound like one.
The Ford modular engine is humongous - many of the same fitment issues as a cammer. Nice to have the overhead cams, though.
I see no point in a Toyota V8. There are many nice engines out there, but getting flat-out weird in your choices serves no good purpose.
Me, given a whopping budget... I'd put a Ferrari V-12 in, oh, a Kirkham.
