Hi Bob,
The mufflers have two 1 3/4" pipes that are next to each other. Both are louvered slightly and each extends in from opposite sides of the muffler and stops short of the other end by about 1-2 inches. Basically it's a 1 3/4" entrance that goes through the louvered pipe into the chamber and then out the louvered pipe next to it. The design is similar to a standard "turbo" muffler.
I don't know how well I explained it, but I hope it helps. If you go to the JCWhitney catalog on line they have an illustration of it under the muffler section.....Wait.. I'll get the URL for them....
http://www.jcwhitney.com/product.jht...D=5448&BQ=jcw2
OK....that will show you better than I can describe them...
Bill