Source for chassis main power?

[Mattchu60]

I'm working on my engine bay wiring for my LS swap. Regarding the connection for the body fuse box main power source - the factory connection is the starter post. With the 5.3 swap I have two additional spots I see i could tap into - there is a junction box for the alternator and also a 2nd positive battery connection that would have gone to the underhood fuse box on the donor vehicle.

I'd like to just install a post terminal for that smaller battery cable and connect there for my chassis (cab) fuse box power source. The wire looks large enough. IS there any issue with this idea? Another option would be tapping into that junction box for the alternator. Are these approved concepts?