Whether the driver are in sync are not the lack of syncopated chuff is not prototypical. I am not sure why people keep alluding to this even if they are in sync on the real thing there will still be a syncopated chuff
I don't think that is true, if by "syncopated chuff" you mean the double chuff that can be heard at low speeds and certain angular mismatches between engines. At several angles the chuff from a simple articulated sounds a lot like a two cylinder locomotive would. It of course depends on the length of the exhaust stacks, so you may actually get double chuffs when both engines match. Remember, there will be four angles, at 90 degrees from each other, that will produce single chuff.
There are no economical ways to simulate this in a scale model except for maybe slightly different gear ratios between engines and sound cams on each engine. You could go to a two motor solution, but most of them involve butchering the boiler and rear cylinder block. Yuk!
Lionmaster semiscale and MTH Rail King articulateds have separate motors for each set of drivers but I don't think this mechanical arrangement would 'scale up' for the full scale versions. It's kind of funny that semiscale engines could actually simulate driver phasing better than full scale ones.
There are some halfway decent YouTube vids of the 3985 where you can clearly hear the exhaust without it getting blown out by the insane amount of whistle yanking you hear in your typical railfan vid. This is a nice example starting around 0:43: