Fascinating find, Douglas!
I don’t know Harvey’s sauce specifically and would like to know more.
There are many similarities to this recipe in contemporary cooking. I am a big fan of Red Boat brand fish sauce (fermented anchovies) and regularily use it in Asian and Mediterranean cooking, often with homemade pink prickly pear vinegar (Opuntia is the source of the scaly parasite harvested for pink cochineal powder). I also use canned anchovies in various sauces such as anchovy infused pestos.
Another household staple is Lea & Perrins Worcestershire Sauce, which shares many common ingredients with Harvey’s sauce: (anchovies, vinegar, soy, garlic, chili extract which serves the same purpose as cayenne). For more info and a 17th century recipe (footnote 5), see
Worcestershire sauce
Good luck with your research Douglas.