Mike Flowerday replaced one of our dash fans a few years ago. He went through the push-release doors near the floor mid-way between the pilot and co-pilot's seats. Of course, he had to pull out the Bose, DISH receiver and satellite-dish control boxes. He reached through the opening, 1 1/2' wide by 1' high.
I think both both dash fans were there, side by side. It took him about 45 minutes by the time he got the doors and boxes out of the way, changed out the dash fan and replaced the boxes and doors.