I've thought about this for a while - not just for fgf's - but for all the cool cars we love from the 50's & 60's.
First issue - safety. The safety standards passed by the federal government have changed in the past 40-50 years. The old design would need a LOT of changes - under the sheet metal if nothing else - just to pass current minimum standards. Think crumple zones.
Second issue - handling. Look - these cars weren't designed to handle even like a Cobalt. To put in a 300hp V8 and have them handle like they did in the 1960's would *really* be putting the safety specs to the test! Think of how the auto journalists would kill the car "lots of power, but handles like a swimming pool!".
Right there you've already encountered a whole lot of engineering redesign. The finished product would look different to the original, even if they tried to keep it close.
Next issue - cost. Are these cars going to be low production cars, or will there be a huge demand from the market for one? And what will they sell it for? V8 sports coupe? $25-30k. Puts it out of the range of the $15-20k Civic/Cobalt buyer.
Now - what *I* would be interested in seeing happen is a private company buy up all the old tooling to make these cars, and set up a factory and produce them under some licensing method using the old specs. Call it a "kit car" or whatever they need to do to avoid the government regulations as well. Then you could order a newly made 1967 Firebird! Now *that* would be pretty cool!
'68 Firebird, 350-4, 2 spd auto, triple black, Dlx Interior