Bachmann Class 47 And 57 Sound Fitting Guide
Start by removing the 6 body screws, there are 8 screws on some class 57's with delner couplings on the cab ends.
Once the screws are removed, the cab door glazing is still clipped to the chassis, use a prising tool to release the clips without the windows falling out.
once inside you'll find plenty of space for a pair of 20x20x7 megabass speakers. These fit with no modifications, and they fit under the fans, theres no need to remove them.
Find the decoder and speakers here:
