Well, this is a bit sobering. I found a page (link below) about harely belt adjustment and they suggest the belt be adjusted just as triumph says, around 1/4" movement with 10 Lbs of pressure. Thats very tight, and if it tightens as much more when hot as it does now with the belt loose, it would be scary tight. I would worry about the output shaft bearing.
I've already gone round and round with alignment, and now tension is going to have me wasting another god knows how many hours trying to get to the bottom of this. Heres a quote from the page...
With a high horsepower engine, it is better to have the belt a little tight rather than loose. A loose belt will break much more readily than a tight one. Most people do not tighten the belt to its proper tension. If you plan on "racing" or hot rodding your bike, invest in a Harley-Davidson BELT TENSION GAUGE (Part No. HD-35381).
It's so hard to get definitive answers today. I could see the adjustment spec they mention being ok, but only if the belt does NOT get tighter when hot.