Sloping top tube?

I'm absolutely sure that building a frame with track geometry but a downward sloping top tube IS possible, I'm in the process of ordering something very similar myself and Landshark make one;

What you can't do is build it with lugs, has to be fillet brazed or tig welded. You say you want a longer head tube, how much longer? Coz obvioulsy having a downward sloping seat tube is going to reduce the hight of the head tube, this might be where you run into difficulty. Good luck and let us all know how you get on :)

I thought it was a fairly basic request, I'm only talking about a couple of inches between the top tube and down tube. The frame will be fillet brazed so the angles shouldnt be a problem. The photoshops give an accurate idea of the head tube in proportion to the rest of the frame, nothing crazy. I was just suprised today to be told that it simply would not work.