Frank,

Forget that trip to the Moon-wer'e going to Mars!!

I have been experimenting myself with exhaust configurations however wit= hout the advantage of a state of the art laboratory!

I have arrived at similar conclusions with regard to muffler, pipe, susp= ension and length. Here is a chronology:

1995-first muffler:
The vehicle, a 1982 Vanagon Westfalia diesel converted to gasoline 91 Je= tta engine. The exhaust manifold, Diesel-the muffler-Diesel.  

The results-loud, and the expensive muffler mounts broke. It was decided= that the pipe diameter was to small for the larger displacement gas engine.= Before changing the exhaust manifold to the 88-92 Jetta one, I replaced the= muffler with a high volume and loud flowmaster, and 2 1/2 "downpipe.

The results: the muffler got so hot it melted a hole in the Diesel oil f= iller pipe, stranding me on the freeway. At the time I didn't realize that t= he engine was experiencing a false air or unmeasured air condition.had to be= towed home, (three days later I discovered the melted hole that prevent the= engine from starting)
Replacing the tube and improving the heat shielding for the tube and the= engine ran again.

The second arrangement was to use a 88-92 G-J exhaust manifold and a sma= ller 2" downpipe was settled for. I got rid of the flowmaster and replaced i= t with a cheap 20 dollar muffler. The results? noise is inexpensive!

I got rid of that muffler, and added a cat, and used a Walker oval muffl= er. It was quieter, but not between 55-65 mph. Over 70 mph, it became quiete= r. resonance was worst right where average speeds were driven. So then I tri= ed using two mufflers end to end-it quieted down, still, there was not enoug= h length of pipe to cool the exhaust gases.
I am now ready to finish the system-it's take 5 years. In the I-4 scratc= h conversion, the Tiico, and others, the muffler gets the least attention.
the Tiico gives you short pipe and a muffler-and it is loud.
What I have now is real funny, but it shoed me something-long pipe is go= od.
I have a custom made Jetta or Golf dual down pipe-it starts at the exhau= st manifold as two pipes the collect four feet down into one. This is routed= directly under my oil pan diagonally to the right rear where it makes a ben= d to the left a goes into a stock 2.1 vanagon muffler in the stock location.=
Since there is only one muffler and no cat, it is not as quiet as with t= he two mufflers-but the resonance is gone. There was a power and mpg increas= e, and it sounds a little racy. I know a shop in a county who will finish my= system like you have described.
I will use the 1993 G-J manifold with dual down pipes that are run rearw= ard about three feet. Will connect with a muffler that has inlet/outlet on t= he same end, and then return back on the right side to the rear and into the= second muffler in the stock location. Six feet of pipe, dual downpipes too = cool the exhaust, and two mufflers to scrub the noise. All without sacrifici= ng flow, but increasing the backpressure some and helping to retain low end = torque are the other benefits.
Now to deal with sound deadening the body from road noise.

Robert K 1982 Westfalia 2.0 Golf lll powered
Seattle