[embee]

Can't answer your questions directly, but FWIW some info on cat exhausts on carb bikes.
The post 2002 Deauville 650 for example had an oxidation catalyst with pulse-air injection and carbs. This however would only address some HC and CO issues at a superficial level.
The chances of an aftermarket fit cat of any description working with unregulated carbs to lower NOx would be slim, it would be essential to avoid any lean excursions. It depends a bit what raw emissions you get from the bike as it stands. If it is purely a NOx issue then running it set richer than normal would lower NOx levels substantially, it could possibly be the difference between passing and not.
You will often see advice such as you can "only" use a cat with EFI, but that is not true. I am not aware, however, of any carb bike set up using reduction catalysts to lower NOx. That was not really the major issue at the time when such arrangements were produced (circa 2002), oxidation of HC+CO was the problem addressed. The formulation of an oxidation cat would probably not work successfully at NOx reduction, slightly different chemistry is usually used, though something designed as a 3-way might just manage something measurable if the bike runs rich. Any free oxygen would inhibit any NOx conversion in those circumstances.
If someone else has done something similar (I'm sure they have somewhere), then any tech info would be invaluable. Ultimately the simplest thing is to buy a compliant bike, but that wasn't the question.