That’s because there are no hard and fast “specs”. Your target gap width should be somewhere between 1/8” - 3/16” after paint to avoid interference issues. When aligning the front end sheet metal, you actually need to start with the doors. Get them aligned in the openings with the quarters and the rocker panels first, then loosely assemble the fenders and hood.
The fenders and hood will all have to be aligned at the same time. Just work slowly and methodically, taking into account what each adjustment will have on the panel(s) ahead of time.
Oh, and bring a boatload of patience, you’re going to need it. In the event that you don’t have enough adjustment to get what you want, you’ll have to “split the difference” between panels and settle for a compromise. Not ideal, but when working within factory limitations, it is what it is.