Hmm. ...Could remove the cassette deck part of the boombox out, cut a hole big enough in the door to fit a MP3 player and glue it in place, graffitti the boombox up a bit, then call it a ghetto blaster and then it actually will live up to it's name.
What funny is that I am actually considering doing this, seeing this guy below sold a few of his crap "HALF ARSED" boxes, but did notice they improve from what he was offering earlier. Except mines will be better builted, as going to design and built the MP3 part to be internal, instead of just taking a off the sheft unit, then add a small display unit somewhere that their a spot available with card reader slot and wire to switches on the box that already their and to the internal amplifer and internal power supply may rebuilt the power supply to handle the addition load, plus thinking about designing it to have a internal harddrive, or SSD to store music, while keeping the original look, might even keep the cassette deck part working and add bluetooth and wifi for steaming.
The second option would be to take his approach and do away with the cassette deck, but instead, add a docking system where the MP3 player or Minidisc player is removable, but when docked it get it power from the box and work with the internal amp with no external wires and let the customer decide which option they want as far as MP3, or minidisc recorder/player, while adding a bluetooth and wifi option for steaming
Here link to his, but his is crap as he run the wires externally to line in jack, "notice the RCA cable" and unit doesn't get power from the box, you need AA battery, which defeats the purpose, of the unit being built in?
http://www.ebay.com/itm/PANASONIC-MINIDISC-BLUETOOTH-MD-BOOMBOX-Ghetto-Blaster-MDLP-LongPlay-Mini-Disc-/261107314883?pt=UK_CE_Cassette_RL&hash=item3ccb3570c3