We feel the pain. My completely stock 68 GMC's sheetmetal fit leaves something to be desired also. But, I have to say that GM was not concerned about these trucks being perfect in those days. They were primarily for work so perfect alignment was not their priority. As these trucks became more of a family vehicle they started putting more emphasis in these areas.
In the meantime, I try to consider it a challenge and not get too frustrated.
I need another beer.