Hi Paul,
Disassembly: Remove speaker grills, then unplug and remove the speakers. Remove all screws holding the unit together (I think there are 6 black screws). Remove the radio knobs, then the nuts from the shafts. There is no glue holding the top to the bottom or shouldn't be unless somebody sealed it after the fact. There are two pieces that clamshell together, go ahead and separate. Now you can pull the radio out.
Inside: There can be a Laminar Antenna, depends on the model. Also, there are two 1/2 thick pieces of foam, one on top of the radio glued to the plastic, and one below. You should also see two foam blocks behind the speakers. Thats about all there is to it. I have seem some units have a ceramic power block on the inside back of the unit.
Radio: You can put in any type of shaft style radio, some you may need a thinner piece of foam on the bottom, depending on the position of the shafts on the radio. Some folks on here cut the unit and put in a single din more modern radio. Personally I would keep it stock if possible. I don't like to cut them up.
Reference:
http://www.vetterowners.com/threads/cyclesound-shells-modern-componets.206/
Pyle Shaft Style Radio Unit - Never used one, not great reviews, but you get the gist.
These are great speakers for the
Cycle Sound Polk Audio DB401
If you have any other questions please ask. I am a Cycle Sound and old radio nut.
I am going to move these posts to their own thread in the Cycle Sound forum.