Velux QVM 156 will not open

I have an old salvage door and was thinking of squaring it up before I build a new frame. However, I noticed that both the hinge and lock side of the stiles are angled ( maybe 5-10 deg off square) so the weather stripping side of the door width is narrower. I checked several modern doors with a square and they all appear to have 90 deg edges. Someone told me this is so the space around the door can be tighter, but I wanted to get other opinions. Should I keep the angle on both sides when I square up the door or should I make all sides 90 degrees? I'm leaning towards simplicity and making the sides all 90 degrees, but then what would the recommended spacing be between the frame and the door?

Have a finished drywall opening, without trim or frame, measuring 83" by 95 1/8". Want to use Stanley 340 pivot hinges and purchase 4 solid core flush primed slabs that are 1 3/8" thick. What size should I order for the slabs?