Hey johnrem46
No its not a difficult job, but you will have to cut up the console or buy a new console made for the newer units.
Most (if not all!) CD players need a fully open DIN sized hole, where-as older cassette tape units had a central rectangular hole (radiused corners) and a couple of round holes each side (for control knobs), like most C3 vettes came with originally.
Another idea! (which I believe is much better), as CD's are a pain in a car anyway (where to store them without scratching, sports car suspension & CD's dont usually mix that well etc), so why not just buy an iPod, with the optional ariel attachment, tune it into a radio station frequency and your away.
The benefits, no moving parts, a huge selection of music (obviously depends on iPod size) and you can use it your house, work or computer as well.
And finally, you dont have to cut up the dash or alter the originality of the car (if thats important!).
Just my $0.02 worth