With those different separate power supplies, do you even need to use a PWR-56 at all in the circuit?  It’s not like there is any encoded signal being put onto the rails like DCC.

No, you do not need a PWR-56 at all. Put 14 to 16 volts on the rails and you are good to go.
The benefits of the PWR-56 are it's repeater function, and its ability to give feedback through the HC about the status of the power system.

Sorry for such a late reply, but I’ve been working nights. I appreciate the offer, but I’m looking into installing this on my own. I’m just trying to figure out. Where can I find the PCB boards that could power the sound board and could take a charge for the battery?

Thanks
Orlando

Nice install and good job shortening the 9-pin wiring and then soldering all of them to the connector plug. Just like a pro!

Progress so far....
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Here's everything pretty much roughly in place.
You can see the four (-4-) wiring harnesses for the lights: fwd headlight, rear headlight, fwd gyralight, rear gyralight.

The Scale Sound Systems speaker is mounted in the rear with a couple pieces of double-sided tape.
All of the other wiring is soldered to the PC Board which is screwed to the two OEM-posts which were used to mount the factory board.

Now I'll use some double-sided tape to mount the LM-3S to the top of the PC Board and start tucking the wires in place.

Good work! Tim Ring told me his team spent months during the design process test-fitting the new 21-pin LM into a wide selection of HO diesels. I highly recommend calling, he is open to discussion and new ideas. Such as, I said it would be useful to be able to apply the brake with the throttle open.