First, I can't claim to be someone who "knows wiring well" but here's my comments anyway.

When I was going through my known original AC wiring many years ago I got all confused looking at the one in the 1968 Firebird Wiring Diagram. I too have a purple wire to the blower motor like yours and that manual shows a "spliced" orange black. Not only did my car not match the diagram, the diagram didn't make electrical sense. Then, I found another diagram in the 1968 Pontiac Diagnosis Manual that appears to be accurate. (Attached)

I personally would not change the routing of the orange/black from the fused alternator connection. I don't know the actual current draw but a 30A fuse implies a hefty one. Adding that draw to some other 12V source would add a significant additional current to the wires feeding it. My 30A fuse holder saw better days so I found an original type holder to duplicate the original appearance. I would assume the blade one you have would be fine.

Finding connectors can be challenging. Somehow harness repro manufacturers find sources. Maybe someone else here will know a source.