Thanks for the suggestions, Andy.

I was able to remove the inner box without too much chaos. Broke off one plastic mounting tab but other than that, no damage. I will definitely be removing the fender to get to what's left of the A/C housing as the last of that is still there, broken away many years ago from it's other part.
Unfortunately, I have to interrupt playtime for a work-related trip out to Cali.

I hate having to be an adult.