Your looking at two decent Thompson guns, both different but known variations. I don't know the seller of the 1928AC and this obviously needs to be researched further. There are no issues with Ruben. Send the money and you will receive the gun upon ATF approval. Period. Sleep well at night.
The pictures provided for both guns are good but sometimes that is not enough. Given the amount of money involved, a quick one day flight to either location to view one or both guns is always a good idea. I believe Ruben will pick you up at the airport if you make arrangements in advance. Not sure about the seller in Ohio but the retail store location is pretty close to Detroit. At Ruben's store you can also inspect the 1928AC Thompson guns he has for sale. That information could aide you if you later decide to view the Ohio 1928AC.
Aside from the technical knowledge needed to make a huge purchase like this, I always suggest the following two rules. Enjoy the search and admire what you buy. This makes the process a lot of fun...as it should be!
TD is exactly right. I checked out a Thompson owned by a board member a couple of months ago. Lucky for me, it was only a three hour drive. But, I was prepared to fly anywhere in the country to view a likely prospect. I'd strongly suggest that you buy Frank Iannamico's excellent book, "American Thunder III." It's a wealth if information and data on military Thompsons. Good luck.