Plug-n-Play decoder, non-Plug-n-Play Loco?

[P5se Camelback]

Well, it sounds like I'll have plenty to keep my brain active until I get a decoder.

I realize all of this is exciting for you diesel guys, but remember, this is a "side project" for me, a way to dip my toes into the pool of DCC and check the "Install" temperature, prior to attacking my roster of more than a dozen Camelbacks, while I also begin construction of a layout! The Alco S-2 is also a little something to take with me when I go visit the local club (30+ miles away) and have something interesting to run on their Digitrax-powered/controlled double deck layout (it's Santa Fe based ... but being a Pennsylvania boy whose freelanced prototype railroad is fairly tightly based on the Reading Company, I just couldn't do Santa Fe! Sorry! No way!)

"Sergeant Slow-Typist" now gets to thank Charlie B. for his first-hand knowledge! I kinda thought they were air tanks! And had I been paying more attention, yes, gotten a bit more intimate with my newest piece of motive power, I would have noticed the filler neck and cap (slightly) visible on the cab "face" in photo number one, above!

[woodone]

Yes, you have taken on a difficult project here. You will be lucky if there is enough room to fit a decoder on the top of the motor.
If you are worried about the decoder shorting on the inside of locomotive- use some .005 thick plastic and put in the inside of the shell were the decoder will fit.
If you are thinking about putting the speaker into the cab you will need to add glazing to the windows. That way the cab will be come an enclosure. If you don’t , you will not get very much volume.
You might want to think about using a TSU-GN series decoder. I say this because it looks like it will be a tight fit to install a capacitor. On the GN boards the cap is on the board, but they do add to the thickness of the board .
You might think about using a smaller speaker and mounting in under the drive lines and letting the sound out the bottom of the unit.
I will be waiting to see your progress. Photos of course!!