I figured whilw I had the bit between the teeth, I'd do some checking on other locos for the fit of these speakers. Just clipping off that mounting bracket that sticks out and no other trimming off one side allowed them to just drop into the long hoods of the Ath SD45 (this version being from the first of the dual RTR/Genesis shells with the sliding cab side windows and better detailing), a P2K GP20 and the Ath SD40's from the latest releases which have chassis that are DCC ready, or sound + DCC. Here's a few more pics, the first showing where I had to clip/file the ribs along the sides of the speaker to get it into the Kato 80MAC, compared to one not so modified, You'll note that doing that mod reveals and removes a very small amount of metal from the edge of the backing of the speaker, not enough I hope to affect it. The protrusions top and bottom form a shallow channel along the side. The shiny edge on the right side one is the metal edge exposed.
The GP20 is from a late run, the chassis probably differs from earlier runs, this one also has LED lighting with the LEDs mounted 1 each end on the chassis. It has a large lighting board and at the back an 8 pin/9 pin DCC quick plug adapter (removed) in the lower recess. Plenty of room for one of these speakers where the lighting board sits and enough room (length) for a Loksound select sound decoder in that back recess after some minor metal removal (pliers and file).
The Athearn RTR DCC ready (it would also be sound ready too, using their speaker which sits in a recess in the rear weight over the truck after removing and discarding the cover which also fills the hole the speaker would occupy and has a thicker lid i.e. adds more weight, lost to having the speaker (which is lousy).
When I replaced the speakers of the 2 with sound ones I have, the iP4s speakers, being about 5.5mm thick over there full length and even without having that metal cover filling the OEM speakers, sat fairly close up under the fans at the back of the shell and also had to made sure they sat hard up against the shell's side, opposite the orifice the sound comes out of them on the side. The iP6s Plus ones, with the sound exit on the end will I think be better, especially too that the opening can be set facing the middle of the loco. It''s shape also, having that end stepped down, can be overhung into the motor's space. Ample room in there for the decoder above the motor. The speaker is just taped down over the weight.