Your firewall cover is a non A/C cover. If you had A/C there would have been an evaporator "suitcase" where my square hole is and taking up a lot of room in the bay. That suitcase housed the evaporator core. By the looks of it, that cover has never been removed. To remove it requires the fender to come off. It's a lot of trouble to go thru OR more likely, just drill two holes and go. That is my opinion.
Maybe as other suggest it had an aftermarket system such as vintage air?
