The turn downs were last used in 67. No chrome or stainless just good old steel turndowns. In 68 Ma went to the rectangular shape loved by most. I have Gibson polished stainless turndowns on my 67 which I purchased from a member here but they're 2 1/2's and tucked nicely under. I know TTI makes the ones your looking for but not sure about 3". My tailpipes are custom bent and had a rub on the spring that had to be rerouted a bit closer to the gas tank which we were trying to avoid just for better piece of mind. 3" will be very tight but should be doable.