Ford 408w stroker. 6.7L small block ftw! You could pull off 600+ rwhp n/a.

Or if you get a real nice Dart block, you could go past the 450 cube range.
Same engine I'm building right now for my stang. I think LSx are just too common cause of all those people who put them in their RX7's. How often do you see an import with a ford engine?
edit: and you could use an aluminum block and save the weight!