As for using concentrate NaCl as a fixer, Talbot never used this for prints from his calotypes. He did attempt it with photogenic drawings as well as his other early experiments. My conversations with Michael Gray, long time curator of Laycock Abbey, informed me that although unhappy with the difference in color, Talbot knew that he had to make concessions if his process was to endure. The use of rapid fixers will definitely change not only the density of the salt print, but also the color.
Jim, thanks for confirming my original statement, as I was trying to give the best advice.