here is a video of a guy setting up the panels and gaps on a task force. he mentions the driver's side cab mount as the pivot and how the cab can be moved around to get the hood or fender to door gaps symmetrical on both sides. he explains a lot and it makes sense if you think of it logically, like lining up a pile of shoe boxes to get even gaps. it is a little bit long but maybe worth the time if you're at that point or doing some major cab work.
it's called:
1955 chevy truck getting put back together"
in case the link fails to deliver.
https://www.youtube.com/watch?v=YmoBtq7lQW8