I have some friends that do just what your talking about. I wanted to go last year and didnt, trying to get squared away for this year.
One carries a lever .308, the other a 30-30 lever. I think more than anything, just because they fit the scabbard better. (Dont know if your horseback or not though...)
Year before last, I think the 30-30 scored. Last year, one got to the tree before the other, ground tied his horse and was going to look at the bear a bit and wait for the other one to get there. The bear came out of the tree and charged. He killed it with his sidearm. I think he said it came to rest at 15'.
Anyway, I asked what I should bring and was told if I didnt have a levergun to go buy a cheap 30-30. Works fine and treed animals arent hard to kill.
Would have been fine last year had he rode up and shot the bear out.
Andy