I used to do historical rendezvous, where you ride dressed in the "fur trade" era and used appropriate dress and tack. The saddle you show has changed very little since the beginning of the 1800's and are used quite a bit. I have an old style "gourd horn" (one with a rounded knob-like horn) which is authentic to the period. It is surprisingly comfortable for horse and rider. Yes, Mexican horses tend to be narrower than American horses, so you must be careful that the tree fits. When looking over the rawhide covered trees, be careful to look for sloppy workmanship. Luckily, you can see almost the entire tree through the fittings.
Here I am teaching a seminar on fur trade era horse tack.
The saddle next to me is an American "Hope" saddle. The gourd horn Mexican saddle is off to the right of it.