Type 55 flour

In the second volume of Julia Child's Mastering the Art of French Cooking (pages 112-113) she says that you can obtain the American equivalent to French type 55 flour by combining 2 parts pastry flour (not cake flour) to 1 part unbleached all purpose flour. This produces a flour with 8 to 9 per cent protein, which she says is best for baguettes.  I want to try this, but I'd first like to know if anyone else has done this, and with what success. 

Thanks, Barbara