The 13-50 yd. number is the recommended distance for SASS main match rifle. Long range rifle could be as long as your range will allow. Keep it reasonable for pistol caliber lever guns (100-200 yds). A lot of cowboy shooters also have single shot guns like Sharps,Rolling Blocks,Trapdoors or H&R Buffalo Classics. For these guns,the range could be increased.
Your rifle is fine for side matches. Remember,that at 200 yds.,the trajectory will be quite high.
Of the two sights that you mentioned,the Marbles is the better choice,as it has windage adjustment as well as elevation,while the Lyman only adjusts for elevation. Whether you need a tang sight depends on how well your current open sights perform out to 200 yds. Some open sights won't adjust high enough to get you on target at that range.
A large loop lever wouldn't be a factor in the long range match,as accuracy is more important than speed. But,a lot of matches will break a tie in total hits with the fastest time.