It's shown in the comics a few times, it just kind of just vanishes or retracts or something.
Later on, when Joe Fixit posessed the body of Bruce Banner in Immortal Hulk and grew a beard and big sideburns, those also vanished when he transformed into the Savage Hulk or later a Red Hulk form (That became a green Hulk form outside the below place/mindscape)
Although in several other cases the Hulk has Banner's hairstyle at the time (Such as when he shaves it bald, long or bearded). Current comics for instance.
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Ford has had a bit of a reputation as a grumpy old man which kind of fits Ross in the comics, certainly.
Although like with Commissioner Gordon and Aunt May he seems to be drawn much younger and fitter (without the Hulk body, that is) than back in the silver age.
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We haven't even seen any footage so you really can't be claiming this.
Just not having the mustache doesn't mean anything, especially when a far more important character trait of Ross is being a gigantic ahole, something that all information tells us is very much being kept.
Don't think Ford is really that much of a draw these days as he used to be.
His most notable films of the past decade have pretty much been the ones where he's reprised past characters (Han, Indy, Deckard) and I think his last big hits as a leading man outside of that was in the late 90's.
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I'm not sure if its stunt casting, I mean I guess, but remember he wouldn't be here at all if Hurt hadn't died.