Roof vent fitment?

[acenjason]

Hi all:) So, I am removing my old roof mounted AC on my 1975 D21. I have a tarp over the motorhome right now because of leaks from around the AC and other places. So, I am taking off the AC and putting in a 14×14 crank vent I am also replacing the crank vent in the bathroom. I will then seal the whole roof. I want to do as much prep as possible before taking off the tarp because of unpredictable weather. Anyway, I took off the bottom of the AC and found a 14 by 14 ,90 degree square hole. Then I took off the bottom of the vent in the bathroom and the hole has rounded corners. Has anyone done this? I have standard 14 inch vents coming in the mail. Will they fit both holes? Will I have gaps on the square  corners the AC hole? Will I have  to cut the round corners of in the bathroom hole to fit a new vent? I looked online and only found one size crank vent. I am very anxious about this. Has anyone done this?