sorry about that first post, after you click that link you have to click driving in the top right then click the full image to see the one i was talking about. my point being that a back lean is common among power hitters. if you start with your head behind the ball keep it there but still shift your weight to your left side. just as you have to keep your spine angle through-out the swing you should also keep the same spine tilt.

i have seen some long drivers that have a lumber jacks stance with the whole body behind the ball and they have a huge lean at impact