Ed K. - I have a Max Gray PRR C1 0-8-0 repowered with a Pittman 9432 driving a NWSL gearbox. The short/fat 9432 fits in fits in the firebox without issue. . After the O scale National Convention I'll drop a TSU4400 in it and see how it does.
Joe - Several years ago using a heavy duty NCE 408SR decoder matched with a sound only decoder was pretty common practice in O scale. Since then higher amperage integrated sound power decoders from Soundtraxx, ESU, and TCS have given O scalers several new options.