Older than 1970s, bucksgtitching was going out by then. The Imperial was their top line of saddles. They seemed to use 2 models, the full Quarter Horse bars and the Semi Quarter Horse bars on the saddle trees. And those models did fit a big range of horse bodies.
Can’t help with the numbers and do not know who owns Tex Tan these days.
At Tack Sales last winter, used Tex Tans went between $350 and $500. Sorry, wish I had better news on the pricing. You can always mark it higher and “bargin” to lower the price! But locally, buckstitching does not sell as well as plain saddles. Tex Tan had good leather and most saddles have worn well over the years, with any kind of care. This one looks nice, probably not too many miles on it because the suede seat is still fluffy, not shiny from rubbing. I always liked the Tex Tans better than Circle Y, because they actually sewed things down instead of nailing the bits to the tree. Saddle strings went thru all the layers to hold things together, not nailed on. Real rawhide covered trees sewn on the wood. Lift the flaps to note the good points to show buyers! Not sure if the Imperials were hand carved, but looking at it closely should tell you that.