If your Bonneville, Grand Prix or Parisienne, or any other model with a full padded dash is cracked beyond repair you may be interested in this. (The Catalina and probably other models do not have a full padded dash)
To my knowledge, in the past, the only way to fix these was to spend $400.00 or $500.00 to have them completely redone.
A company in Reno http://www.dashtop.com/
has a relatively inexpensive solution.
They produce a hard vinly like "skin" or "dash top" that is installed over the original padded dash. No need to remove the old one but you may need to take off the high spots if yours is in really bad shape.
Granted it will not be padded any more but all the ones I have seen look just like the originals.
They are produced in black only and you can paint to the color of your choice.
The do not currently produce one for the 1963 Pontiac (I believe it will fit the 1964 as well) but in April of 2004 I took them a good original and they said they would make a mold and get it in production.
They were supposed to pull a trial one and send it to me to try out, some time this week.
Keep your eyes on this site for further developments.