Definitely only the top portion of the dash need be removed. If you are good at removing screws you can't see you can get it out by removing only the mid-dash pad (the one with the AC vents).
Be very careful when removing either part of the dash pad since they become brittle with age and can crack easily. Push and pull gently and make sure you don't do anything to bend them, such as holding it by one end instead of in the middle. Same is true of the AC vents themselves.
First unscrew the time set knob. To do this use two small vise grips, one to hold the shaft from turning and one to unscrew the knob off the shaft. Use a thin piece of rubber, like perhaps a bit of rubber shelf liner, to keep from scratching anything.
The clock is held to the upper dash pad with two screws that point up. If memory serves they have 5/16 inch hex heads.
The clock has one power connection and one light socket plugged into the back.
-mB