It doesn't matter where the horn wire is connected as long as it's hot at all times, so you can honk to let your date know you're there to pick her up after turning off the engine.
On the 48-49 wiring diagram, the horn power is connected to an isolated terminal on the fuse block, then to the downstream side of the ammeter. The horn button wire also connects to an isolated terminal on the fuse block on the way to the button. On the 50-51 wiring diagram the horn feed connects directly to the downstream side of the ammeter, and the horn button wire also connects directly from the horn to the button.
To make a copper bus bar, you could get a piece of scrap copper pipe and cut it open and flatten it.
