I would assume your stock system is similar to the 66 Birds, so the first thing you should know is, stay as far away from custom autosound as you can.
Way too many horror stories concerning quality of work, and quality of sound.
Most companies that say they convert your stock radio to a modern design, are using custom autosound products.
Now, if you are more interested in originality, I can't help you, but if you care to alter your dash as I did, then click on this link and see what was involved in putting in my new audio system.
I gotta tell you, the sound is incredible, and worth every minute it took me to install it.
LOVEfords Forum
Bob.