You are correct. It basically does just say to remove the heater core. However, one thing he is over looking is it says to remove the HVAC housing and then remove the core.
I attached the process on how to remove the assembly and once that is out remove the heater core is much easier.
Let us know if you have more questions and we can figure out what to do next. Thanks
Images (Click to enlarge)
Sunday, June 28th, 2020 AT 7:25 PM