Without out going inside,
The 95-96 theftlock impala am fm cassette could run an Ipod adapter through the factory aux plug.
The 95-96 am fm cd could not.
If a person wanted am fm cd that could the last year or two (2000-2002) Camaro -S10 radio looked the same and was capable.
This is what I have with a PAC plug in adapter.
On a good day it would work seamlessly controling the ipod from the radio.
Some days it will get moody and the ipod has to be unpluged and reset, so to speak.
It would always play, just sometimes control from the radio face was lost.
A quick search comes up with little.
Seems they might not make the adapters anymore .
As for going inside the radio to make direct connection, I have nothing to offer.