Wow, that is actually a really good find. I just had a quick read but it looks quite detailed and I may use it next time I try tuning.
Another suggestion is VVV Worm's tuning guide on the official Forza forums which is easily found by searching VVV Worm in to Google, I think the information in that guide has been broken down a bit more to make it more simple but there is a lack of pictures to help explain.
I have no idea what I'm doing when I'm tuning so mainly use the explanations given within Forza.