I would agree it was a fording kit. I looked through lots of pictures, but cannot find a rear view of the Sexton II or a radial engined Sherman with the fording kit. There is a side view here.
http://www.ramtank.ca/sexton.htm 130 is a very interesting vehicle. There are so many subtle differences from the more common late production vehicles. Notice the rear engine deck is not hinged in the middle, but both pieces bolted in place. No hole for the binnicle, rivets galore, mufflers on the engine. Probably originally had Sherman type tracks. This was probably a combat veteran, but the privious owner sandblasted all the markings off. Alex, I'm flattered, but Sexton engine guru I am not. Jesse.