The reason they were restricted from going to Silverton was the weight restriction on one of the bridges up the canyon. This was remedied when Mr Bradshaw bought the line and reinforced it.
As for tractive effort....I heard that the K-36, 37 and so on actually stood for the tractive effort....so a 28 would have 28,000 lbs, a 36, 36,000lbs and a 37....well you get the idea. I think this is not far off. I have the historic preservation study that detailed some of that and I will see if I can find it unless someone else gets there first.