I just bought a stainless dual exhaust from Ram Air Restoration (RARE). It is 304 stainless with stainless mufflers as well, I decided to go with 2 1/2" and it has been great (orig. is 2 1/4). Since I have a convertible with the cross brace, I could not do a cross-over without shimming the X-brace down which will weaken stiffness. This system is not true original set-up with the transverse muffler.
Also offering original set-ups was Classic Exhaust, they advertise in Hemmings. Hope that helps.