I was perusing Al Gore's inter-web and found this. https://www.jefflilly.com/build-tips/36-door-fit/ Thought it did a good job showing how you go the extra mile for the fit and finish gets that improved overall look.
Something that I have noticed on our old cars is this issue needs to get revisited for time to time after completion. I don't know if there is a garage gremlin that moves body panels around at night or if it's part of shake rattle and roll but things move around over time. The thing is if you have it correct before paint it will come back much easier down the road.
There is a whole section of tips for body work on their site, good stuff! Thanks https://www.jefflilly.com/build-tips/
@Johnboy34 beat me to it... It is one of my saved favorites. Don't know when I'll need that info, but I have it! If only I could duplicate some of it!