These are advertised as fitting 68 to 72 Chevelle but I didn't check the Chevelle book.

However the Beaumont book lists part #3956756 group 3.705 as being Extension, Muffler. 

It goes on to describe it as fitting 1969 / 396 Eng exc dual chambered exhaust / muffler tail pipe /

                                                 1969 / 396 eng with dual chambered exhaust / rear /

I would guess its a newly manufactured but GM approved part Says 10 available.

https://www.kijiji.ca/v-classic-cars/kitchener-waterloo/1968-to-1972-chevelle/1538759181