Here is what NADA Classic Cars says about a 1970 Chevelle 2 door SS 396- I added a cowl hood in the event it might have had one: (I'm not interested in those cars and don't know much about them, just wanted to try to give it as high a value as possible.)
PRICING
Original MSRP: $2,662 Low Retail Average Retail Value High Retail
Base Price $3,975 $7,300 $10,050
Options
396 V8 Engine 50% 50% 50%
Chevelle Super Sport Cowl Induction $200 $400 $600
TOTAL PRICE $6,163 $11,350 $15,675
I just don't think anyone is going to spend $3-4K for a VIN number and cowl tag to make a clone of a car that would only be worth $16k tops.
Even so, for another example, lets say I saw a really valuable car that might fetch $60-70k at auction, and (LOL) I had a lot of money to piss away and was interested in it. Now I might not be the brightest star in the sky, but if I were to bid on that car I might just spend a few thousand dollars (a drop in the bucket) extra to have an expert from Hemmings or ? come to the preview with me and authenticate the car. I imagine a not so valuable clone with swapped tags trying to be passed off as the real McCoy would be recognized quickly by an expert, and I wouldn't be out too much.
I think a clone is worth what it is regardless if it has swapped "authentic number" tags or not. But in turn, I imagine quite a few undeucated suckers with a lot of money have been ripped off along the way too.
-UT-