heater core replacement

Hi All, Baptism by fire, my first big project is replacing my heater core... I pulled apart my dash and got to the core, but my new one is one inch in width, while my installed one is over two inches wide (pictures attached). I looked at other parts shops and they all seem to have one inch...

TL/DR do I have to pull out dash to get to the HVAC actuators/doors? Not sure I am using the right works but the various flaps that control fresh/vs recycled and hear vs AC. Also any NC recs for someone who can do these repairs? The buttons on the HVAC panel are also due to a refresh and I...