This is the best place I have found to get the 'real deal' as far as how to remove and install something complex like a heater core on on a Crown Vic. I hope that you realize that, most likely you will have to empty the A/C and remove the entire dash. (I used to work as a Ford Dealership tech) so allow lots of time and patience. Take pictures of the steps and write notes down. It is SO easy to forget.!
here is the link-> http://bit.ly/alldata_repair_manuals it costs a few bucks but is the most reliable info. I use All Data in the Shop