Door opening

[EricSean]

So I am getting ready to replace my body mounts this winter and where the windshield frame and vent window frame meet the gap gets wider towards the top. Tells me the firewall is leaning forward a little bit which also makes the gap to the back of my drivers door wider than it should be. My question is does anyone know if there is a way I could find out what the door opening should be front to back? Should it be the same measurement at the top as it is at the bottom? I have measured the drivers side and did find that the opening is almost 3/4 of an inch wider at the top compared to the bottom. Any help would be appreciated.