If by running pants you include tights, then try Nike. I am about half an inch shorter than you but with similar length legs. If you means looser pants, then no idea at all because I wouldn't run in such garments
I am just over 6'3" and about 11.5 stones, (varies between under 11 stones nothing and about 11 stones 12 pounds, depending on the time of year), have been about this for years and it isn't a problem. I eat what I like, when I like, no faffing about with funny diets. Make the most of it, people only want you fatter to reduce their feeling of guilt.
When I was in my 20s I was 10 stones, again, not a problem, but muscle mass went up with cycling & running
I have a pair of black Fred Perry leather "plimsolls". Apart from the rubber rand all around them they are hardly distinguishable from normal shoes, and that hardly notices. The sole is somewhat harder than normal plimsolls.