How do I install an aftermarket CD/Receiver?

Specifically, how does an aftermarket unit fit into the space taken up by the OEM head unit? Is there a facia kit or is the opening the same size? I have a 1999 C280 sport (carbon fiber trim).

Can someone give me advice or point me to a thread that addresses this? I'm having a little trouble finding anything in the forum.

Thanks much. Dan

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2003 Hyundai Santa Fe, Silver
1999 C280 Sport, Black
1997 Ford Escort, Toreador Red