I've had a go with this picture editor thingy, here's hoping I've done it even though I've been pratting for ages without knowing what I'm doing. I think I've lost 1 photo by altering one and saving it over another. Anyway lets hope this works.
This should be a picture of the cut down speaker fitted where the rear coupling fits between the frames. This involves removing the lug where the coupling screw houses by drilling/filing, the speaker wires go through the remains of this hole after lining the inside of the frames with insulating tape to insulate the speaker connections from the chassis. You need to file a groove in the top of the chassis to take the wires from exiting this hole to where they will run up the back of the motor housing where there is room for this because of the body fixing pillar. After wiring up the speaker to the decoder this should hold the speaker roughly in place to allow the rear body fixing screw to be fitted, the speaker then half covers this screw before being held tightly in place by the new rear coupling wedging it, I then filled the small gaps in with black-tack to seal everything.
Fitting the speaker here frees a bit more room for the decoder. I used a Plux 16 Zimo decoder I took out of a Fleischmann loco, this goes at the front of the motor housing, it justs needs the two small retaining lugs breaking off and the plastic locating bit at the bottom removing so the decoder sits on top of the cylinder block. Not trying to fit the speaker here means there is room to construct a plug affair for the decoder, I used a female fitting plug cut down from a dead 21 pin decoder linked to the 4-pin plug on the loco's wiring, if you use a wired decoder you could connect direct to this plug. I didn't find it neccessary to alter the body in any way, everything fitted back ok.
The decoder is held in place/insulated with black-tack between the decoder and the motor housing. The pictures show the speaker wiring going down the side of the motor but this was a mistake I realised after the photo's were taken, the wires need to go over the top of the motor.
Here's hoping this has come out OK, and you all understand my ramblings.