Assembling and lining up a front clip can be a maddening experience for sure. The few I've helped with, we always left ALL the bolts very loose (including the rad support bushing/bolts). Start working everything around till you get close and start snugging up hardware a little at a time. Just like bolting down a cylinder head or a wheel, work around all the bolts slowly till you get very close to everything being tight. The last ones you want to tighten are the rad support bushings. But we all know these trucks were never great to start with, you'll never have perfect gaps without adding metal in certain areas and taking away in others.
For reference, here's a few pictures of our shop truck ('76) and my personal '85 and their gaps. The got vastly better with the '81-up trucks. You can see how different the 2 sides are at the A-pillar.
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach