Mike, you may want to talk to Jim Dietrich at Dietrich Chemicals. They sell similar restoration products and are very good at working with you one-on-one over the phone or by email - more so than Prosoco. I really can't tell by the picture what the main problem is - soot or whatever. That affects significantly the type of chemical to use. In most cases you will want to test 2-4 materials and see what it will take to get the cleaning accomplished.
I have been looking at doing restoration work, and if you can give me any tips on how to find this type of business they would be appreciated. Bill