I made-up a rear section with a Magnaflow stainless steel muffler and a chrome tip I found at a local autoparts store. A little black wrinkle paint, some red tape, a little bit of orange and an ANSA decal and, Voila! A rear ANSA box for a spider.
If that facebook links for you, there is a step-by-step showing the process.
It also has an actual ANSA center box and header. Not too loud though the thinness of the header seems to make it sound a little gravely. I may put the cast set-up back on at some point.
The Magnaflow number is 10444 for a 2" core and 10414 for a 2-1/2" core. Both are 2" In and Out. I used the 10444.
http://www.summitracing.com/parts/mpe-10444/overview/