One of my gripes about Soundbugs. They include a 1-inch round speaker, that basically will not fit in anything but a tender or a dummy engine. Why not skip the speaker, cut the cost a couple of bucks and let people know they need to buy a speaker that fits the engine?
Yes, you need to get a speaker that fits, probably an oval one. Then, you need a speaker enclosure. Unfortunately, the enclosure makes the space problem even more critical. You can home-build an enclosure, which might be the right thing to do in tight situations.
I put a Tsunami into a P2K GP9, basically the same engine, a couple of months back. I should have photographed the installation, but I didn't. What I did was mill out some of the weight around the cab opening and mount the speaker and enclosure facing down over the cab-end truck. I built my own enclosure out of styrene and glued it all together with the speaker to eliminate air-leaks. This was a long and tedious process, by the way. On the other hand, I really like the results.