I have tore down to the heater core with dash top removed, how far do you have to go to remove the core. It appears the a/c unit has to be removed. Am I missing something?

 

Came across your post as I’m experiencing strong coolant smell inside my car (2010 Mazda 3 2.5 manual trans). No smell outside, just inside passenger compartment.
Prime suspect would be heater core. Wondering if that’s why you replaced yours.
Looks like a ton of labor involved.
Any videos or step by step instruction s out there?
Any and all advice welcome!