I received one of the sound units a few days ago and so far it has performed very well. However, as I was preparing to do a shell swap with an older Rock Island unit I realized that I'd had a senior moment when ordering the new one and wound up getting one that had a gray fuel tank and trucks instead of the required black and so had to send it back.
From what I can tell, the shells and truck sideframe / bottomplate details are identical between the two versions (despite the radically different chasses) -

Conversely, the fuel tanks
are completely different between the two as far as how they attach to the chassis and I don't think they will swap (which is why I had to return mine) -

The real bitch is swapping out the cab light guts as they have changed rather drastically. Previously, you had these two parts that got their photons from the decoder board -

And now you have this wired up little goodie instead -

Getting that stuff out of the cabs so that you can swap them is a huge pain. And at this point I'm not even sure how I did it. Basically I just poked and pried in trial and error fashion until they finally popped out. So, now I just need to wait for my replacement unit so that I can (hopefully) complete the swap.
-Mark