Yes. Unlike Johnson, Louis had modern punching technique and more importantly, fights at his era were fought at intense pace compared to the past. Grant's right cross might trouble him a bit, but eventually Louis breaks through and finishes him quick
This ends quickly either way. I'd have to favour Louis' sharper punches to get the job done but Grant would impose his physicality more than say Primo Carnera and probably hurt Louis at some point in proceedings. Louis KO 3.
I don't think so. Though I think there's maybe something to be said for a change in style thats come about with much bigger and more well padded gloves. Louis fought to make every punch really count, it was far more judicious than you see today because the stakes were higher with 5, 6oz gloves. It wouldn't work as well with 10, 12oz gloves. Just a vomit of speculation on my part, that admittedly.