It was a mistake when we went 442 against Arsenal last time, but considering we're at Old Trafford and Arsenal will likely be very weakened, I can see us playing it. Cleverley and Welbeck don't deserve to be dropped, their second half against Spurs was fantastic. But the likes of Giggs, Park, Carrick, and Hernández need to play. On principal it's hard to leave these players out, especially when most of them have had good games against Arsenal in the past.
Fergie doesn't like to play an unchanged side, but I can really see it happening in this match. Basically no one who started against Spurs deserves to be dropped and fitness won't be an issue at this stage.
However, I won't be surprised if the one change is Carrick in for Welbeck and we play 433. It's just the more tried and trusted system against Arsenal and we almost always beat them with it in recent history. Giggs & Park do deserves a shout at getting in, but they're only likely to come in, in favour of Cleverley/Anderson or Young.
If Welbeck doesn't start, I think Berbatov will be left out of a 'big game' yet again. That'll pose even more question marks. Maybe the freshness of Giggs, Park, Valencia, and Berbatov will come into play after the international games, due to them not being involved (Valencia may, but I'd doubt it).