very easy. just one tip to give you. to remove those little black clips use a pair of nettel nose and stick the tip of them inbetween the base and the head of the clip, then open the pliers and they will pop right off.
Also, when reinstalling the core, it's best to have a 2nd pair of hands. You'll need one person under the dash to push the core up and thru the firewall, and another person under the hood to help guide and grab it. The whole job shouldn't take more than an hour.