Exhaust option
I found these Superior exhaust extentions at Pep Boys.  They will fit in the collector box if the old mufflers are cut off at the welds.  some trimming of the small ends of the extentions will be needed to make it fit properly before the pipe is welded on.  Also, you can reuse your old hanger if you cut it off the muffler and have it tack-welded to the new pipe.
You will have to fabricate baffles to fit the pipes. I think a simple way to do it would be to make end plates that fit inside the tubes like the Mac baffles use. They look similar to the plastic end caps used in mailing tubes.  you would use one at each end of the baffle and secure the inner one with a bolt thru the bottom backside of the muffler and baffle "cap"
Hopefully you can see from the above pic that creating the baffle is simply a matter of having a tube welded to a resonator mounted to a round, fairly tight fitting steel plate. the end caps would take a bit more fabrication to add a mounting flange, poss welding on some 3 1/4 OD pipe.  the inner pipes can then be drilled with perforations, and even fiberglass or stainless steel wool added to deaden sound, etc.
The pipes at Pep Boys were only wrapped in celophane, not on a card.
Click  pic to see full size image
Above is the baffle design, it is a straight pipe with a resinator at the end.  this is a simple design & inexpensive to build. the perf baffle is wraped in Stainless steel wool rather than regular steel wool which would rust out pretty quick.  The SS wool will eventually need replacing, depending on how fast it "soots" up.  I got this design from "Monyt's Honda Tourer page, exhaust mods"   It is a very interesting page on how he went through several steps to experiment with different baffle setup.  I decieded to start with what worked best from him. The forward end of the inlet pipe should be capped off and the forward end plate should be drilled extensivly to allow exhaust gasses into the baffle.

Muffler Case:
see PepBoys, above

Stainless Steel Wool:
McMaster-Carr Supply Co.
in the search box in the upper left frame: 7364T19
stainless steel wool, 1 Lb roll  4" W x 1/4" thick x Approx 22 feet long
Price (as of 4/02) $15.78 
Prices have changed since this page was posted

Inner Baffle Pipe:
I'm using 10" x 1 1/2  I.D pipe and shortened 2" adapters for the resonator, (for a total length of 14") but you can use whatever I. D. & length you prefer
I'll add more pics with the stainless steel wool wrap and the muffler attached to the collector box as I get there.
Note: I never finished this project as I ended up buying a Mac System & a SpecII system for the spare Vision...