When I had my first run Accucraft C16 quite a time back time back, I replaced the original Pittman motor, as not only was it too fast, it also did not have the grunt that I needed.
I installed a 1:60.5 and although it did make things very s-s-s-l-l-o-o-w-w. it did increase the pulling power one heck of a lot. I then replaced that with a, I think 1:38, geared Pittman. That was a good compromise.
I am not sure if the C19 is the same as the C16... I suspect that it might well be different as the C16 was one of Accucraft's first electric 1:20.3 rod locos (with the K27) and they improved their building techniques later.
It was a little bit of a palaver stripping the loco down, but it is pretty straightforward as long as you take photos of each stage so as you go, especially the handrail and piping into the cab.
This is the help that was given to me on the MLS forum:
"Now look inside the cab. The first thing to do inside is to take the nuts off where the handrails enter from the front. You can then slide the handrails forward and out of the way. Put the nuts back on the end of the handrails so you do not lose them. Now along the bottom of each side are some bolts and nuts that hold the cab on (these are what Kevin was talking about). You will need to remove all of them. On some models the nuts are behind or just above details under the floorboards. Be careful of the piping as you pull the cab off.
At the front of the boiler pull the braces out of the smokebox. They are just a press fit into holes in the smokebox and the deck. Now pull of the smokebox front, it is just pressed in and will come out with a little persuasion. Inside the smokebox you will find the board for the headlight on a bolt. Remove the nut and lift the board off the bolt. Push it out of the way. You do not need to unsolder any wires unless you are rewiring everything and then you are on your own
.
The rest of the work is best done with the loco upside down. I built a cradle to hold it steady, but you can do whatever you want. At the bottom of the smokebox is a curved nut that holds the boiler down. The other end of the bolt is the one the front truck slides on. so first remove the bolt the front truck pivots on. Now holding the curved bolt inside the boiler remove the other bolt for the front truck. One last bolt to remove. If you look between (I think) the second and third driver axles you should see a screw head. If you look inside the boiler you will where where it comes through and is held on by a nut. Remove this bolt and you should be able to lift the boiler off and access everything. "
Unfortunately I sold my C16 a few years back so have not got it at hand to check the bolt placings etc.
I have got the later C16 with updated and also a C&S 2-8-0
good luck!