Damn, I can't see the last vid because of bs copyright claims!
The first two vids show, at least in my definition, hook type punches.
Marciano used a lot of "leaning in" to potentiate the power output of his hooks.
Most people who tend to lean much often rely on this because of poor technique and can be countered brutally by a proficient boxer.
It's often seen as a unclean brawling technique.
However, Marciano really knew how to combine his defensive movement with leaning in to increase power.
I see the main difference between hooks and overhands in the arc of attack:
Hook punches follow a somewhat horizontal curve while the overhand strike has more of diagonal character.
Since the fist travels from behind (which makes technical, boxing aficionados sneer ) and above the head, it's effectively more of a thrust because you can dodge way more easily laterally.
The overhand is often employed to maximum effect after it's reaches it's apex, contrary to about 50% of all hooks. (Technically, you could call that a downward hook and some styles -some kyokushinkai schools, for instance- even use this rather exotic punch at very close range - it looks weird with the ellbow high in the air. Not sure what to think of this)
Many of Chuck Liddell's overhand right KOs landed like that, ie they were delivered to hit during the fist's descent and they didn't travel horizontal - that's way they're not hooks in my book.
Such a blow has to be timed and placed very accuratly. You have a hard time landing this against someone who evades laterally, in contrast to hooks.
I admit that it's hard defining those things because there is a lot of groundwork to be done - classical boxing doesn't differentiate a lot of strikes!
I'm all ears to hear your take.