I know I wouldn't run a drivetrain w/chainline that's 3mm off for sure. Especially not if I have the oppurtunity to get it right because I haven't bought the parts yet.
Are integrated cranks that narrow? That's 7 mm in compared to standard sqare taper stuff...
I'd look into the Level thing. If you don't mind the proprietary system and don't want to run a freewheel, you're golden. Otherwise, just respace an IRO if you don't want to run a flipflop. Actually, I think you can get pretty good chainline if you run a freewheel on the other side. Freewheels are wider than cogs.