I can get the feel, but not the same delicate images. I can create grain, but that is part of the equation. The original autochromes had potato starch that was died and outlined with carbon black. I can duplicate the color grains by adding noise and pointillising the image, but I can't get the black outline around the "grains" created in CS5.
I shall keep working on it, but until then here are two images in the style at least to keep me contented that I am on the right track. Once I nail it I'll post the step by step it took me to get there.