The rear muffler is sort of an odd configuration in the context of modern cars, as it is a long, round muffler. That might be tough to find in an off-the-shelf SS variant. The closest match I've seen in format are mufflers for 80's US pickups, which aren't much of a market for the SS guys. That's why most people who want SS buy from a supplier of OEM-style like W&N.
Exhaust is an area where I don't even pretend to care about originality; the rear muffler on my car was replaced with a straight-through spec'd as a Camaro resonator, and I'm planning to replace the burned out front resonator with a pair of long, slender straight-through's mounted parallel. It sounds like a Jag XK, and I don't see a thing wrong with that!
I get the attraction of SS, but -- the original factory rear muffler lasted 30 years and the resonator lasted 36. I'll be lucky if I live that much longer, so the next owner can pony up for the SS system... 8)
