Well Jack, we've got the answer. I still think that it's a possibility to remove the sprocket through the hole. without taking the cover off using a pair of hemostats to slide the sprocket off (so long as you can get enough slack in the chain). It would be good to try than avenue and then if you can't, take the cover off entirely. Doing it that way, you don't have to disturb the valve timing at all. I believe I'd align the static timing marks and then pull the sprocket. That explains the 27Nm torque value too. The big hex nut isn't torque'd at all. It's just a means of holding the crank while you tighten the the SHCS
If it indeed will come through the hole it would be a time saver and a cheap (relative) fix.
What we really need to know is at what VIN number at at what point in time, year and month, did Triumph change the design and implement the new sprocket/key in production models?
We are assuming sometime in '06 but exactly when in '06 and what unit number. That's the question.