The "where it is pic" has no relevance for you, because you are installing the Classic Update, correct?
The horn relay function is performed by the horn relay provided in the Update kit; the buss bar function (all the other connections shown in the "where it is pic" and in factory wiring diagrams) is not used by the Update kit. Power distribution in the Update kit is different and arguably (I'm sure some GM engineeer somewhere would argue theirs was better) more efficient and straightforward.
The hardest part of the Update kit is having to cast aside your OE diagrams and OE harnesses and trust and follow the directions. I got hung up too, and because I am a knothead engineer, spent over an hour on the phone with Donny Bock at AAW while he explained all the circuits and how they had been improved from factory routing. I have all my notes, but can't get to them because I am temporarily wheelchair bound.
So, again to answer what I think is your question, you do not need the OE horn relay that mounts on the driver side radiator support with an AAW Classic Update kit. The kit supplies a small, modern relay for the horn circuit, and you'll end up mounting it somewhere inside the car near the instrument panel. Any other wires on the OE hron relay buss (like the alternator lead, power window/accessory feed, etc) will come from other parts of the Classic Update kit.
Trust the instructions, and when in doubt ask here or talk to Donny Bock at AAW (call and ask for him, and tell him you got his name here). He's forgotten more than I will ever know