ac-heater case removal

well I have a heater core leaking on the floor and drain tube plugged. I have removed every thing on and in dash to get to the case. looking at it with that cross bar in front of case how are you suppose to get the case out. I have removed even the lower part of the case where the 2 vents that are rusted now. the main case wont come out as a whole. and when I do get it out how are you going to put it back in. I know i'm going to break something. I have googled about heater case removal but it seems no one has done this. any one has an idea about this. and yes i'm checking on a case replacement. thanks for reading this.