Hmmmm,  so every OEM exhaust is the best possible design, mandrel bent,
with well designed mufflers?  There's overwhelming evidence to support the
statement that most OEM systems have lots of room for improvement.
Inevitably one will cite the latest BMW M3 or something as an example where
there is little improvement to be made...but not too many of us own one.

My experience with VW is that you can purchase a complete replacement
exhaust, in mandrel bent stainless, from a reputable vendor, for less then
OEM.

www.ssheaders.com may still make an exhaust for the vanagon in stainless.
I'd check them out.