In my 80 ton 3 truck shays I used a SoundTraxx decoder. Decoder part number 884006 and speaker, part number 810112. I removed the circuit board in the tender and direct wired the decoder. I have found that this eliminates a lot of headaches that could show up with the board left in. I cut some of the oil tank bottom off and drilled some holes in the bottom of the bunker to let the sound out, and installed the speaker in there.
Hope that helps.
Hope that helps.