I just hooked up an iPhone 8 speaker. amazing sound from such a small device!
I cut off the mounting tabs. I believe they have no other function.
I cut away the plastic at what I will call the bottom of the speaker--the part that has the small port in it that probably fits into a recess inside the phone housing.
first I cut the +/- 1/8" protrusion on the side of the speaker that is mostly plastic. I think the protrusion is a resonance chamber which I'm sure is important in the phone. but not so much for my loco. with the top of the chamber off, I saw that I could safely cut about 1/4" towards the metal housing.
to my ear, using one the stock sounds in an LM-1, the horn and bell sound the same as with the unaltered speaker.
so, you can slim the speaker down by about 1/8" and shorten it about 1/4". not much but might be just enough in some situations.
I also just ordered an iPhone 7 speaker as a comparison with the 8. I can't find dimensions online, but it looks like it might be smaller. only $2.29 free shipping from California so I should have in in a week.
ken