I do all my trail riding in an english-type endurance saddle:
I personally don't care for a horn, so agree with the people suggesting you think about a hornless option.
I also don't care for the wide fenders typically found on a western saddle, as they bother my knees no matter how much they are turned. Not sure if having more narrow fenders would be an option.
The other thing that jumped out at me was the stirrups. Like Celeste, I ride in the EZ ride nylon stirrups and love them. I wonder about using aluminum though.. is that so light that people can't keep them on their feet (this is a complaint I have heard from english riders using lightweight aluminum irons)? Or do most of the people using those types of stirrups ride with their feet "home" so slipping out isn't an issue?
Yes I could definitely narrow the fenders good idea :)
Also I know what you mean about the light weight aluminium stirrups but these ones are fairly heavy so don't think feet would slip out but I like your idea about wider stirrups, I think they'd be more comfortable and feel more secure