Here's the sad part. Any of you body guys would know that when you buy a repro sheet metal part, it always has to be worked if you want it strait. I don't think it'd be any different with one of these due to shipping, handling, manufacturing and negligence on "people's" part. This is not a bad idea, in fact, it's quite cool IMO. As stated above, most of the cars that look great and are over 40 years of age have some form of aftermarket parts on them and if you have one aftermerket part then you might as well have the whole shell cause it's not considered a "pure" car at that point.
This is a very pricey start tho that will require a lot more than you may think to get it right. The last full resto that we did was a 69 Buick GS Stage1 and yes it was a real Stage1. We replaced one quarter and just worked the rest of the car and that guy ended up with a bill just over $11,000 and that was a deal IMO considering it was a frame off job. All I'm saying is if you dump $15,000 in the shell alone, plan on spending another $10,000+ for the paint work. That's if you have a good hood, fenders, cowl panel cover, lower valence panel and wheel wells, which by the way you had to pay for already so that has to be figured into the price.
It's a great concept and if you have money to burn, do it. Else I would suggest finding a descent car to start with. Again, this is all my opinion and I'm not in any way trying to step on anyone's toes or rain on your parade.
Josh
Edit: I listed this incorrectly. It was actually a stage 1 GS not a GSX. We were looking back through pics of some old jobs that we did and I called it a GSX and my dad was swift to correct me on the fact that the GSX didn't come out until 70. Sorry for the mistake.