The exhaust on my 87 V8 Astro is a dual 2.5" setup using Hedman 68600 medium length headers (1 3/4" primaries, 3" collectors) and Flowmaster 3-chamber mufflers. The exhaust exits on each corner under the rear bumper.
In the picture, you can see the driver side header. A small modification was required to the driver side "V8 Engine Mount Adapter" to allow use of these headers. The image was taken from behind the front left tire, looking up and towards the front of the engine. The letters in the picture show the following points:
A = Primary tube for cylinder #1 and where the engine mount interfered
B = Driver side collector is just out of the picture
C = Engine mount adapter, cut along blue dots, yellow shows original shape
D = Stock lower engine mount/rubber isolator and frame perch
E = Steering shaft coupler
Another interesting side note.. Just out of the picture to the left of the "E" is where the emergency brake cable (metalic) runs. This cable makes contact with the plastic spedometer cable in this area. It's less than four inches from the primary tube "A" to this E-Brake cable, which results in a good deal of heat transfer. While this won't hurt the metal E-brake cable, it will melt your speedometer cable and stop it from working. It's a good idea to plan for this by seperating those two cables (they both go through the same holding clip in this area) or insulating them. Speedo cables are only $8.99 for Astro's by the way!
This picture is a collage of captures I made of the entire exhaust system from front to back. Kind of reminds me of the Mars Pathfinder pictures! Notice the driver side exhaust crossing under the drive shaft and running alongside the passenger side exhaust into the pair of 3 Chamber Flowmasters. Out of the picture, the tail pipes are routed to their respective exit locations under the corners of the rear bumper.