With regards to basic empty weight and unusable fuel.  If you install your
pickups properly you can have less than three quarts of unuseable fuel in
five tanks. ie header, two mains and two separate wingtip tanks.  I agree
with the previous post that a header tank method can empty out themain
tanks.  As a matter of practicality.  I have not done that.   These birds
get there fast and 3.5, 4 hours is a long time on your touchy.

Bob Smiley
N94RJ