Update:
Today I restored the speakers and, although it was another new experience for me, it went well.
Existing speaker is on the left with the doner on the right (a 2nd
Panasonic RX-C41L I bought cheaply for spares).
The speakers may appear different sizes but this is not the case. One seems larger because the wider part of the
speaker is closer to the camera lens.
New speakers wired & soldered, secured in position and ready for case assembly.
The original speakers had the same foam pad over the wires arrangement so this was replicated
with fresh foam & double sided tape each side of the wire to keep it all snug.
There is a post on the opposing side of the casing that sits against this to keep everything in place securely:
Here's the finished result, I feel that replacing the creamy white colour of the cones with black on this box has given the box
a more solid appearance. It's a low-end box so it needed all the help it could get!
*There is a slight difference in the width of the Sharp and Panasonic speakers used but the difference probably does not exceed 1mm at a guess, it really is a tiny difference. Although the Panasonic speakers sat neatly in their new Sharp speaker cases home, the Sharp speakers were just a tad too tight to secure into the Panasonic case. I'd guess the minimum amount of filing on the two opposing side edges would take care of this if your back was against the wall.