Dale -
Is all the sheetmetal you have GM, aftermarket, or a combination?
The new body shells are kind of neat, but because they are all import stampings and not welded the way GM did them, they can be spotted as non-original. On the plus side, if you get them from someone who has good jigs, makes quality wleds, and generally has good quality control, they may actually be better than GM.
It's kind of the same deal with using an original shell but replacing the majority of the panels with aftermarket panels. It's going to be obvious what's been replaced, no matter how good the install is, because the parts are just different in subtle ways.
Ideally, you'd reuse your shell with your partial VINs intact, using GM replacement panels stamped with original stamping tools, yada yada yada. If you collected a bunch of NOS sheetmetal, lucky you, but otherwise this option is pricey enough to scare away all but the deepest pockets.
Just a painful situation...