I acquired all the guts of a Lionchief Plus 2.0 Doodlebug, and conveniently had a Railking Protosound 1 model sitting around. It seemed like a perfect combination. I had heard that the LC+2.0 Doodlebug only had one motor because the second motor wouldn't fit with the smoke unit. I love a challenge, so I did some measurements. There would be a bit of work involved, but I couldn't see why both wouldn't fit.
In order to provide a mount for the stock Lionel smoke unit, I put some brass hex standoffs onto the mount and then epoxied those into place in the shell screwed to the smoke unit and bracket. I also made a gasket for around the stack exhausts and of course drilled them out as they were not functional on the Railking model. Once the epoxy cured, I removed the smoke unit and added a little more to strengthen the mounting, it's pretty secure now.
The one thing I'm not crazy about is how the LC+ 2.0 board manages the marker lights, they only turn one set on based on direction. I think I may change the front markers to red and reverse their operation for a more reasonable operation.
Here's the smoke unit mounted with the cab face back in. It took some trimming of the cab face mounting to fit the smoke unit in, it is a pretty right fit.
Next I mounded the speaker, made an aluminum mounting bracket for the LC+ 2.0 board and mounted it. I added a switch (after the picture), so I have PGM/RUN and Smoke ON/OFF. I elected to just let Bluetooth be enabled all the time, it really isn't a big deal, and if that ever annoys me, I'll jumper it off. I just didn't feel like drilling holes for another switch. 
Here's the completed chassis prior to adding passengers. I used very narrow LED strips to provide LED lighting for the passengers, they're powered using one of my LED regulator modules from track power. I had to shorten the front interior panels from the stock look, they used to surround the front motor. However, they got in the way of the new smoke unit, so they had to go. OTOH, I didn't want the electronics showing through the baggage doors, so I hacked the front panel to at least cover those.
Here's the finished product, ready to start revenue service.
A quick drive-by video. As you can see, the smoke unit works, and I retained both motors.
