Keep in mind that if you use a sloping top tube frame, be sure the seatpost is long enough to penetrate the frame to proper depth.
If you use a short seatpost (to save weight or add strength) make sure you get it long enough to meet required depth I don't recall off hand but it may be 2 inches below top tube. If not, you can damage the frame itself as the seatpost will act as a fulcrum causing damage to the seat tupe collar area.