Good luck! I put a micro Tsunami in a Spectrum 2-10-0. To make room for it and the speaker I wanted to use, I needed to pull the weight out, along with the circuit board. You'll definitely want to include the capacitor for the micro-T.
Looking at the diagram for the Climax, it looks like they've left space in the bunker, and the bottom of the bunker is drilled out for the speaker. I'd stick the biggest speaker I could get to fit in there (be sure it's an 8 ohm one) and hope you can squeeze the micro-T on top of it. I think I'd probably wind up pulling the PCB out, just for more space, and more volume for the speaker.
I haven't taken the Climax apart, but my guess is that your biggest problem is going to be finding room for an adequate speaker.
