A Sountrax Tsunami or micro Tsunami would be the way to go, the heavy steam version has the correct sounds, you even have whistle and air horn like the prototype. I'm more interested in how a sound decoder and speaker will fit in the tender with Kato designing it for one of their own slot-in decoders. A photo of the tender without the shell would be good to see.
There is plenty of room in a kato GS-4 tender, the weight is directed more toward the bottom of the tender. As for hooking the decoder up you can just use one of Kato's DCC decoders made just for the GS-4 to run motor control and the lights and use a micro tsunami for the sound. Im not sure how good the motor control is with their decoder is, Im sure its not as good as a lenz decoder but it is easier to hook up, you just replace the pc board in the tender with the DCC decoder from kato and presto thats it. then all ya have to do is solder the two wires on the micro tsunami onto the correct pickups.
I converted mine using the Kato DCC for motor control and adding Tsunami sound. The following link is a complete conversion. http://www.trainboard.com/grapevine...ami-install-Step-by-step!&p=479435#post479435 Harold
I have installed several of the Tsunami's into this locomotive. First off I will warn you that ALL units are NOT DCC friendly! I now isolate the motors in all of the units I do. I run two wires between the tender (decoder) and the loco for the motor. Before doing this I had several decoder failures do to the drivers hitting the motor frames. I also have not found it necessary to remove any weight. I mount the decoder on the top of the weight. The weight will act as a heat sink. I do as UP Phil did for the speaker install, but I just machine a small semi-circle of material at the speaker end to make room for the speaker enclosure. This leaves over 90% of the weight in its original place. The decoder and speaker and it capacitor will add some weight as well. The sound is very good and loud. I have had to turn the master volume down as it was too loud.
