I installed dual Dutra duals on my `84 D100 and can tell you, it made a lot of difference! I went with the duals instead of just the front because my original was cracked; not just in the usual spot, but around the heat flapper. Was just easier.

I concur with Dan about driving it to the muffler shop without an exhaust: don't do it! I bought some flexi pipe and bolted that on temporarily; at least the noise and heat exited at my feet. Of course, my muffler shop is only 2 miles from the house...

As for the rest of my exhaust, it dumps into 2.5" pipes that Y into a single 2.5" pipe just aft of the clutch linkage, then cross over into a single Smithy's muffler that exhales through a 2" pipe that terminates in front of the rear tire. The reason I did this was to keep the flow velocity high, and it works well. If I drove by and you were blindfolded, you'd be hard pressed to tell if it was a D100 or a TR-6 that went by. Deep rumbly exhaust on deceleration, zero popping. No rasp at all, except when I hammer down, and even then it's not so loud I can't converse at normal levels.

If you do go with dual Dutras, be prepared to get a mini starter, grind a notch off the block (super easy with a Dremel), and you'll need a masochist to install the starter with the exhaust in place.

Anyhoo, my $0.02

_________________
If it was easy, everybody would be doing it.