some people make a big *** deal out of it to the point where they sound ridiculous. Buy some vin rivets from either ebay or FABO member cuda junction (they are not cheap) and then put your dash of choice in and rivet your vin back on.
easy, so boogie man will come and take your car and there is nothing illegal about it provided you keep the same vin number on the same car. You can not use a dart vin number or any other number. Make sure the vin tag that came on your duster stays on your duster. easy as that.
I have a 68 dart and I swapped in a 68 Barracuda dash. I did exactly what I am describing and the original tag that came with my dart stayed on my dart. Except now I have a rally dash. Its now several years after the fact and my car is still is still in my driveway and no FBI or boogie men have come looking for it.