Oh the challange!
I have an 0-4-0 Anna. Best guess is that it is close to a 1:20.3 Locomotive.
It needs the weight so unless you remove the lead weight in the saddle tank batteries will likely take a trailing car. You could place batteries in the Cab but it would not look very good.
Instead I will use a supper capasitor.
Plans are to install the decoder, backup power, and SUSI sound.
Taking it apart is rather simple. You need to remove the 6 screws holding the Cab and then there are 2 screws on the inside side of the cylenders holding the boiler down.
I think I will have time over the weekend to do this.
May bring it to the NMRA National for my clinic.
More later when I do the conversion.
Stan