Well, first off, and to be a bit of sticklier, the right cross and overhand right are NOT the same punch, though they CAN be.
The overhand tends to have the elbow a bit higher and may "loop" a bit more as opposed to the cross that SHOULD come in straight with the elbow "down".
Of course in practice it's hard to distinguish one from the other.
Louis was a boxer, not a WC man, so we should ask ourselves why we need to use a fighter from a different MA to show WC.
I am guilt of this too though, I like to use Tyson as an example of what Hung Kuen would look like in the ring.
I shouldn't because Tyson doesn't do HK anymore than Louis does WC.
THAT said though, you are quite correct that Louis does indeed use some of the principles of WC.
Why?
Because the human body only works the way it works when doing a specific task.
Louis has many things similar to WC because he is fighting HOW one fights WHEN applying those principles, principles that are NOT exclusive to WC.
Psalms 144:1
Praise be my Lord my Rock,
He trains my hands for war, my fingers for battle !