That had a sound system. called the Mighty Sounds of Steam...If the tender is with it, don't run it until you inspect and replace the foam the sound board sits on. Those boards short out on the tender frames as the foam deteriorated over time. The capacitors go bad too. There is a thether wire to the tender, I don't recall if it's the chuff switch or power to the tender, but is one of the two, or both. The rest is just like any other similar loco, any basic diagram applies to the motor, smoke, and light. Finding rebuilt boards is possible, but installing new sound is a huge step up from that static generator stuff and IMO worth the extra cost in end result compared to spending 60%+ on a repair. The first thing to do if the board is dead or dying would be replace all the caps.
I think ADX Rob or GRJ posted something in the way of electrical on the " sound of steam " boards a few years ago. Use the advanced search in the upper left "hamburger menu" (stacked blue lines) and you might pull it up pretty easy.
On parts, often there is only one parts breakdown on a loco type. Other similar trains must refer it also.
I.E., You may need to look for the Nichole Plate 4-4-2 of that time. If there are parts that only appear on the Milwaukee, it is usually noted on the NP diagram. I'd look at C&O, NYC, Santa Fe and NP as possible alternates for that loco.
("NQDY" Nichole 
. Been a while since I thought of her. I guess maybe she did lose.. 
...RIP Dearie , I'll run cab forward for ya tonight!)
