Adding a bunch of wires to the starter solenoid and using the solenoid as an electrical junction terminal is a bad idea.
Adding a bunch of wires to the battery cable clamp is another bad idea.
A junction block next to the battery, specifically intended to connect all the wires together is much better. A small battery cable pig-tail, feeding the junction block serves as a fusible link.
Your charging wire has a Blue segment at the end that is a fusible link connection. If the Blue segment is nicely installed, you could just connect it to the junction block.
If the other Red wire in the drawing is long enough, connect it to the battery junction block. Later additions such as relays for head lights and fans can be tied to this junction block.
Your Vintage Air calls for two 12 volt power sources. The 30 Amp breaker can be tied to this junction block. The other 12 volt source would be from a Switched fuse, in your fuse block.
None of that junk should be hanging off the battery cable clamp or starter solenoid.
You already have two wires on the Alt Bat terminal. That little jumper wire SHOULD NOT be there for a correctly wired SI Alternator. SI terminal #2 should be connected to the Battery Junction Block. SI terminal #2 is the battery Sensing wire for the voltage regulator, inside the SI alternator.
You can now put the RED wire from the firewall connector on the Alt Bat terminal. That puts you back at two wires on the Bat terminal.
Remember, that's the Red wire that is probably too short to reach the Battery Junction Block and is closer to where GM had it anyway.
I'm not 100% sure that you understand, YOU CANNOT USE THAT DN ALTERNATOR,THAT YOU HAVE PICTURED, WIRED IN THAT FASHION.
YOU MUST REPLACE IT WITH A SI ALTERNATOR.
The alternative is to add an external regulator and several wires.