Heljan/EFE Class 35 'Hymek' Sound
We fitted sound to this EFE (made by Heljan) Hymek using one of our 30x17x4mm speakers, this gives a great sound and is very easy to install.
As with the 33, if there is a lot of metal behind the sockets under the speaker you may need to trim them a bit, this can be done with a pair of side cutters (image shows a 33).
Find the sound decoder here and the tools here.