Here's a pic of the stock factory Corvette exhaust Dan in Pasadena modified for his build. I believe the come on the C5 Vette. IIRC the double wall goes all the way down to the dump flange
They normally have an EGR? port on them and I just made an aluminum cover when I used them, but I suppose you could spend some time grinding the tube off and filling and smoothing the manifold.