I think that most people have the wrong idea regarding the McClellan saddle.
A McClellan 12 is about the same as a today's 15 to 16 western cut. I'm 6' ~ 195 lbs and it fits fine. Now if you have a broad beam, thats another issue. The 12 was universal and met the needs of the majority of soldiers and almost any breed of horse.
The saddle is extremely comfortable and is similar to a Peruvian saddle and somewhat like an Australian rig. Unlike a western saddle, the McClellan is bare bones and extremely light. The bars are well padded and rides well even on a high withered horse.
Typically, I use a custom 16 inch western cut set on a mexican charro tree which is probably the most comfortable of saddles for extended trail riding (8 to 14 hours), however, I prefer the McClellan for endurance and steep mountain riding.