[Boss 5.0]

What gap is huge? The door to quarter? I'm not very clear on what you are asking based on what you typed.

I always start at the rear and get the quarters fit to the trunk, then to the doors. Then move to the front fenders lining up with the doors and the hood.

If what you are saying is that your door to rocker gap is perfect, but the quarter to door gap is too big. Then see if you can slide the door back more? Or is the door gap uneven to the quarter? Then at that point cutting and splicing is a needed operation.