I managed to squeeze a 3.5mm (1/8" in old money) stereo socket between the HS button and the Cassette flap.. Its a very tight squeeze.
While it was all apart, I also took out the grains of wheat bulbs inside the LCD display and replaced them with Tri Colour LEDs and their associated resistors to limit the voltage and current else the LEDS will pop..
I did blow the green section of one accidentally so the Pic with the Green display is only list one side..
The Camera doesnt really give it justice but its an Idea.. Btw the time on the clock is actual..

Couple of pics at the end show the Jack socket and my Ipod Touch plugged in.
One important note here.: The Cassette amplifier circuit is noisy in that there is a degree of background hiss always present. You dont notice it on the Tape because there is a mute circuit till the tape is inserted and music plays.. With a MP3 player mod I have had to disable the mute circuit so there is a little hiss till the music plays. This would primarily be noticed on headphones at slow speed when no music is playing. Also if the input was used for GPS .. Slight hiss till instructions.. However, several GPS's are also mp3 players and some are "connected" to the web too.. That would help eliminate the quiet spells..

Green

Bit of Fun.

Blue

Red

Assembled

Unlit Assembled Blue
