1968 barracuda formula "s"
You may be better off trying to fix your dash. Being that your car as stated is a Formula S and the VIN tag (which will show if it is a 340 or 383 car) is part of a 68 dash you will need to swap vins.
On a normal car... /6 or 318 V8 it really wouldn't matter but people will question non-correct vin rivets on a Formula S car.
If your dash simply can not be fixed you will need to try to find the correct rivets. I think they are made but I'm not sure who you can get them from...
Others on here may know.