Hello, I just thought I would put in my 2 cents.
I also highly doubt they were lippizaners.
My guess would be an old variant of the Percheron breed or another similar draft. It is my understanding that many breeds have changed in appearance greatly in the past 200-100 years. (Which would explain why they are a bit "lighter" in stature than a modern day Percheron). That being said it would be logical for a draft horse of that time to be lighter than those of today because they would need to be used both as draft animals and also under saddle as it is was expensive to have multiple horses to fit different purposes. These horses have no feathering on their feet, so that rules out Shires or Clydesdale for the most part which are also common drafts. Also Percherons are commonly grey.
You might all ready know this so please forgive me if I am stating the obvious but the photo looks like these are canal horses that were used to pull boats from paths along the water way. I know that they were much more common in Europe but I am not mistaken they were also used in Ohio quite a bit. Maybe you can see if there is a equestrian or canal museum that might have more information.