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.

Clean.  I particularly like the PBM-2 at the front.  Nice use of space.

LVRR1856 I began the investment in Raipro about 6 and a half years ago and have been very pleased with my choice. As we head into the colder months I plan my usual conversion from DC to Railpro for up to 10 locomotives while sitting by the fireplace. At this time it does seem that everyone I look out is out of stock of even the WH-9 wiring harnesses which is what I need to get started and takes most of the time to install. I have faith that a new stock will come in before the new year so I can do my next batch. I have about 70 locomotives and this should be the second to last batch I need to convert if I can stop my nasty habit of buying more locomotives.

I generally bought everything from William at Precision Design and have been very happy, but am excited to be looking to make my purchases from Scale Sound as I have purchased many speakers from them. Not sure if the tariffs are slowing the delivery of new stock of LM3's but I am hopeful that they will be plentiful again by December. I am not at all worried about Ring Engineering going the way of Betamax or Polaroid and understand that there are sometimes supply chain issues.

What you might want to consider is leaving your DCC units be for now and going forward install Railpro in the unconverted locomotives with a yearly plan of what is reasonable for your budget and time. By the time you get 10 of those non-DCC locomotives running Railpro you will quickly make plans to remove the DCC from your existing locomotives and make the switch. You can run you Railpro trains on your DCC track so you can still have both for now. Once you complete the installation of the last of your non-DCC locomotives you will want to continue working backwards into the DCC trains by changing out your decoders to LM3's. This is a compromise without giving up your DCC (for now) trains as they will all work on the same tracks but you won't be able to MU the Railpro with the DCC locomotives unless you want to drive yourself crazy. I hope this gives you some encouragement to take a step into the nice warm Railpro water while still being in DCC water. 

Hey Rob,

That sounds pretty good! Give it a whirl.