I have been running a belt drive for about 35 years on my 850 with no problems. I use two adjusters to maintain alignment of the belt. I was back in England visiting my parents so I took advantage, and the day off to drive up to Staffordshire and bought a lot of stuff from Norvil. Les Emery came to the counter for a chat and told me how to set up his kit. Run the belt at idle with no side plate on and adjust it to run true. that way you aren't relying on the belt being held in place by the side plates, then install the plate. On the way home I felt like dropping into a pub for a pie and a pint only to discover that they still closed the pubs from 2-5! Bless 'em
Nobody has mentioned that the way to set up the tension of the primary drive be it chain or belt is to make the primary too tight and then adjust if forward to the desired tension. This takes up all of the slack in the set up otherwise the gear box will get torqued backwards and tighten the belt or chain. The only problem I've had was last year a piece of the clutch tab washer broke off and ended up in the belt. I found it on a maintenance check before there was too much damage but I do need a new front pulley. I have had problems over the years with the original set up and now use a belleville washer (spring) with the nut torqued to 45 ft/lbs and blue loctite. I find it amusing that a broken part could lead to 7 pages of discussion on all of the engineering variables of belt and chain drives when the answer is to replace it and move on.
I hope I don't sound too pi**y but I've spent the last few days refurbishing the rear disc brake of a 1978 Triumph. There should be a special place in hell for whoever designed that piece of *&#$#%.