These shells on the SC-44 and ALC-42 are not that easy to take off but I managed. I'll admit I'm a novice and I was being extra careful.
They do indeed appear to be the exact same 17736 chassis but the inside of the shells differ quite a bit.
The SC-44 has the upper and lower LEDs on the front of the stock light board. So the DN163K4B could be a contender as sundowner mentioned.
The ALC-42 came stock with the additional light decoder for the engine compartment. No such luck on the SC-44. But that was advertised as needing the light decoder added.
I'm probably going to wait a bit and see if Digitrax updates their site based on their response to my inquiry.
I took some pics but apparently cannot post pictures here. Probably because I'm a newbie. "An Error Has Occurred! You are not allowed to add a picture."