I stayed with 12 gauge for the battery charging wire across the top of the radiator because it will not be carrying the full current load when the engine is off so it doesn't need to be 8 gauge. If I was going to have a stereo amp then I would have used 8 gauge in order to play the music with the engine off.
I re-wired mine with the terminal block on the core support and separated the four soldered wires and rejoined them on the block as shown
here.
It's about the same as yours except that I joined my brown wire from the cab block to the brown wire that goes to the alternator no.1 terminal, and I joined the red sensor wire to the red sensor wire that goes to the no. 2 terminal on the alternator. This enabled me to eliminate the external voltage regulator and
I think you will be very happy with your setup.