OT: Hacking line inputs into old boom boxes

[CCartCat at aol.com]

I'm considering putting line inputs into one or more of a collection of 
partially departed boomboxs (dysfunctional cassette transports, mostly).  

The oh-heck-why-not-blow-it-up/bent circuit method would seem to be wiring 
into the inputs as if to replace the cassette play head.  I was wondering 
about other relatively quick & dirty approaches.  Perhaps some sensible ones 
as well, tho' still on the side of simplicity.  As I have no great need for 
the radio, tips on tapping the line inputs into the radio would be great.  
All this would be without benefit of schematics, so any clues are welcome.  
And I would likely run them on AC, so tho' I already know to stay away from 
the power supply, any safety tips (std. disclaimer applying of course) also 
welcome.

I'm a lurker with basic to intermediate grasp of electronics (have built fuzz 
boxes, LFO's from scratch, a kit or two, etc.).  Just trying to eek a little 
crazy lo-fi functionality out of these devices rather than heap them into the 
landfill.  Suggestions?

Thanks,
Kevin Seward