...Months later... Sorry, I thought I was set up to receive notifications, but I wasn't.
Thanks for the input. I agree that the wingnuts may have been a problem in real-world use.
It seems to me that the saddle could have been used for taking measurements. Maybe it could have been adjusted to a particular horse, then measurements taken to build a tree. I'm still not entirely certain. Over a hundred and thirty years after the patent date, I'm not sure I'll ever find out any more details. I guess it's a keeper.