Maybe this will help.
I started the cut the opening gap about 5/8" and trimmed it as I got the frame into alignment. The forward (point) of the cut has to be far enough forward to allow the glass to lay well.
edit: Thought I'd mention that when making the cuts & welding I made sure not to lose the (2) screw holes that hold the Plastic Triangle panel on at the top, it helped when it came time to fitting & modify that piece.
You will also need to make a relief cut in the upper A Pillar to allow a bend radius.
A few pics of the body work at the lower A pillar
Choptop, Vertical Door Hinges
Lowered Suspension w/ 13" Brake Disk
CarPC - WinXP Pro (GT Sport Edition)
+ a lot more.....
[This message has been edited by Orig88GT-NC (edited 03-07-2015).]